The Anatomy of Hemideina thoracica.
[Read before the Wellington Philosophical Society, 28th October, 1925; received by Editor, 31st December, 1925; issued separately, 17th February, 1927.
Plates 55, 56.
Hemideina thoracica White.
Deinacrida thoracica White, Voy “Erebus & Terror,” vol. 2, Insects, pl. 5, f. 2, 1846. Deinacrida megacephala Buller, Zoologist, vol. 2, p. 850, 1867; Trans. N.Z. Inst., vol. 3, p. 34, 1870. Hemideina thoracica Walker, Cat. Derm. Salt. Br. Mus., part 1, p. 161, 1869: Butler, Voy. “Erebus & Terror,” vol. 2, Insects, p. 25, 1874. Deinacrida ligata Brunner, Verh. zoolbot. Ges., Wien, vol. 38, 1888. Deinacrida megacephala Hudson, Man. N.Z. Ento., 1892. Hemideina megacephala Hutton, Trans. N.Z. Inst., vol. 29, 1897. Hemideina thoracica Kirby, Syn. Cat. Orthoptera Br. Mus., vol. 2, p. 115, 1906.
Hemideina thoracica is a member of the family Stenopelmatidae, tribe Locustidae, order Orthoptera. The Stenopelmatidae are characterized by the following points: long maxillary palpi; compressed tarsi, the first and second joints of which are without lateral appendages, mostly provided with pulvilli; fore-tibiae often with foramina, above with apical spines on each margin; hind-tibiae above with single, below with two apical spines on both margins. The family Stenopelmatidae is divided into two sub-families (1) the Anastostominae, or those provided with pulvilli on the lower surfaces of the tarsi, to which sub-family Hemideina belongs, and (2) the Dolichopodinae, or those without any pulvilli. The Anostostominae are further subdivided according to the presence or absence of auditory pits (foramina) on the fore-tibiae. Auditory pits (foramina) are present in Hemideina.
According to Tepper, 1892, the Stenopelmatidae are represented in all continents, being best developed in Africa and North America, the Australian region furnishing only a moderate variety. The family contains thirty-eight genera and ninety-four species. Of these, eleven genera and eighteen species are found only in Australia and Polynesia. Hemideina is restricted to Australia and New Zealand, but, according to Brunner (quoted by Hutton, 1896), occurs also on Lord Howe Island.
The New Zealand members of the Stenopelmatidae are commonly known by their Maori name of Weta. They are nocturnal insects and live in burrows, made in trees by other insects which they enlarge.
At night they can be heard making their characteristic sound, which resembles that of a match being scratched on the roughened surface of a match box. Both sexes possess “ears” and stridulating organs, so no doubt they call to one another. They also make this sound when irritated or annoyed. The hind legs are raised high above the body, the insect standing firmly on the first and second pairs of legs, and then the hind legs are brought smartly down, rubbing against the file on the abdomen and thus producing the sound. Their food appears to consist chiefly of wood and leaves. They will eat apples and sugar, and they are sometimes cannibalistic, eating one another, when the ventral surface of the abdomen is the part usually attacked. Parasites which prey upon the weta, include mites, which are found upon the softer parts of the exoskeleton, and Nematodes and Gregarines which occur in the mesenteron. Wetas may be found in rangiora (Brachyglottis rangiora), tea-tree (Leptospermum), mahoe (Melicytus), beech (Nothofagus) kawakawa (Macropiper), and others. They are often found in dead wood and under loose bark. Certain of the wetas are cave-inhabitating,—not, however, Hemideina.
I wish to express my thanks for assistance and advice to Professor Kirk and to Mr. David Miller, Government Entomologist.
The Head-capsule. (Fig. 4). The head capsule is arched above and flat before. A median white line extends over the epicranium nearly to the level of the antennae, where it forks, the arms of the
Fig. 4.—Head-capsule viewed from before with front and epicranium removed to expose tentorium.
Acl and Pcl, ante-and post-clypeus; CE, cut edge of capsule; Gi, articulation of ginglymus; In, mouth of invagination forming anterior tentorial arm; La, labrum; Md, mandible; Oc, occiput; Oc.F., occipital foramen; Oc.Iv., invagination on occiput extending dorsad from acetabulum; T.A., and TP, ant. and post. arms of tentorium; T, body of tentorium; Tr., trochantin of mandible.
fork being very short and diverging only slightly. This inverted Y-shaped suture must represent the epicranial suture of other orthopterous insects (e.g. Blatta), but in this case the anterior arms are very much reduced and evanescent (Fig. 25). The anterior arms are on a ridge and between them is a small elongate slightly-depressed area. The ocelli are frequently wanting in the Locustidae. They are represented in Hemideina by minute pale coloured circular areas. The lateral ocelli are situated one to the outside of each anterior arm of the epicranial suture. Below these, between the antennae and carried on a projection of the front, is the median ocellus. The compound eyes are pear-shaped. Each is surrounded by a chitinous ring, the ocular sclerite, which is more prominent on the median than on the lateral aspect. There is a small white area at the dorsal end of each eye. The antennae are situated to the inner side of and partly below the compound eyes. At the base of each antenna is a chitinous ring, the antennal sclerite, most prominent on the median aspect. The basal joint of each antenna articulates with a laterally-placed process on the antennal sclerite and is connected all round to the antennal selerite by a membraneous area. The basal joint is long and cylindrical, the second shorter, the third longer than the second but shorter than the first, and the remainder small. The antennae themselves are as long as and longer than the body.
The front is limited distally by the invaginations forming the anterior arms of the tentorium, laterally by a ridge extending on each side from the base of the compound eye to the above-mentioned invagination and directed slightly outwards, while proximally a median projection of the front extending a short distance between the antennae bears the median ocellus. In the male, the lateral ridges (frontal ridges of Hutton) are rugose and blackened. In the male there is also, on the front, a pair of depressions, one to the inner side of each lateral ridge. The clypeus is separated from the front by the above-mentioned invaginations on each side, but for about the median third of its breadth is continuous with the front, the suture being obsolete. The clypeus is divided transversely into post-clypeus and ante-clypeus. On each side the post-clypeus is confluent with the trochantin of the mandible. At the junction on each side of trochantin and post-clypeus is a concave process for articulation with the ginglymus of the mandible. The ante-clypeus is white and membraneous and has two small chitinous plates in a transverse line. It can be withdrawn under the post-clypeus, thus raising the labrum which it carries. The gena forms the side-wall of the capsule. It is limited from the front by the lateral ridge of the front, and from the trochantin of the mandible by the invagination forming the anterior arm of the tentorium. No sutures separate it from the epicranial or occipital regions. The posterior surface of the capsule is the occipital region, adjoining and enclosing the occipital foramen. On each side the occiput carries an acetabulum in which the condyle of the mandible works. From this acetabulum, an invagination or apodeme extends dorsally along the occiput for a short distance. Surrounding the occipital foramen on each side is a rim, with whose ventral end the cardo of the first maxilla articulates. At about half its length
the rim is divided by an invagination. Between this rim and the occipital wall is an invagination to form the posterior arm of the tentorium. According to Comstock and Cochi (1902) this rim would represent the posterior sclerite (epimeron) of the maxillary pleurite, the anterior sclerite (episternum) being absent here. The tentorium or internal skeleton of the head is formed by an anterior and a posterior pair of arms, which meet and fuse, forming a central plate, the body of the tentorium. The arms are formed as invaginations of the body-wall. The mouths of the invaginations forming the anterior arms can be well seen in Hemideina. Each is a transverse slit extending a short distance between front and post-clypeus on the anterior surface of the head, and continued on to the lateral surface where it separates the gena from the trochantin of the mandible. As the mouth has such an extent, an anterior arm is at first wide and fan like, but soon narrows. The invaginations to form the posterior arms are smaller. The mouth of each is situated above the cardo of the first maxilla between the rim at the lateral margin of the occipital foramen and the occiput. Anterior and posterior arms meet, forming a narrow plate, the body of the tentorium, which forms the lower margin of the occipital foramen. Between this structure and the margin of the submentum is a space through which the nerve cord passes.
Fig. 5.—Head of male viewed from behind to show mouth parts.
Ca., cardo; Cond., condyle of mandible; G, galea; Lac. lacinia; L.P., labial palp; M., mentum; Md, mandible; Mx.P., maxilliary palp; Oc., occiput; Oc.F., occipital foramen; Oc.Iv., invagination extending dorsad from acetabulum; P., palpifer of labial palp.; Pg., paraglossa; P.M., Prementum; Rim., rim at side of occipital foramen; S.G., sub-galea; S.M., sub-mentum; St., stipes; Tent, tentorium.
Mouth parts. (Fig. 5.) The labrum is carried by the anteclypeus. It is ovate and its distal margin is notched in the middle line. Its under-surface has a median groove and on each side of the groove is thickly clothed with hairs, nearly all of which are directed towards the groove. The under-surfaces of the labrum and clypeus constitute the epipharynx. At the level of the clypeolabral suture the epipharynx carries a transverse sclerite, with which is connected on each side a small chitinous framework. The under surface of the ante-clypeus is less thickly clothed with hairs and has a median groove, which is separated from that of the under surface of the labrum by the transverse sclerite mentioned.
The paired mandibles are stout and strongly chitinized. In the male they are immense, and the size of the head-capsule is correspondingly enlarged to provide attachment and room for the muscles working them. Thus results the often grotesque appearance of the male, the size of the head being out of all proportion to the rest of the body. A mandible in cross-section is roughly triangular, presenting anterior, external (lateral), and posterior surfaces, and an internal edge whose distal half is toothed. At the apex is a bifid tooth, followed by a single tooth, this followed by a tooth with three cusps. The proximal half of the internal edge carries a number of hairs. Proximally there is a blunt projection on the posterior surface of the mandible. In conjunction with its fellow, it forms a crushing or grinding apparatus for the food. The abductor muscle is inserted on a small chitinous process arising from the proximal margin of the external (lateral) surface, the adductor on a large chitinous process arising from the proximal end of the internal ridge. Between mandible and gena is a small transverse sclerite, the trochantin of the mandible, limited from the gena by the invagination forming an anterior arm of the tentorium. The trochantin of the mandible is continuous with the post-clypeus. The mandible articulates with the head-capsule by an anterior ginglymus and a posterior condyle. The ginglymus articulates with a concave process situated at the point where post-clypeus and mandibular trochantin merge into one another. The condyle articulates with an acetabulum on the ventral margin of the occiput. Behind the mandibles are the paired maxillae. The basal part of each maxilla consists of cardo and stipes. The cardo is a roughlytriangular plate, transversely placed. It articulates with the end of the rim, which bounds the lateral margin of the occipital foramen. The stipes is oblong in shape and vertically placed. Externally the stipes carries the five-segmented maxillary palp. The first two segments are short, the last three long and the last club-shaped. No palpifer is present. Internally the stipes carries the lacinia and the galea. At the tip of the lacinia is a befid spine, and just below this is a movable or articulated spine. The internal surface of the lacinia has numerous hairs. The galea is two-jointed, the proximal joint or sub-galea being short and slightly swollen, the distal joint elongated and provided at its tip with an indentation for the tip of the lacinia to rest in.
Behind the first maxillae are the fused second maxillae, constituting the labium. The sub-mentum is large and articulates also with
the ends of the rims mentioned. It articulates with a smaller mentum. Before the mentum is a still smaller pre-mentum, deeply cleft in the middle line. On each side of the pre-mentum is a palifer, which has the form of a ring incomplete ventrally. Each palifer carries a three-segmented labial palp, the last segment of which is club-shaped. Before the pre-mentum are the paired laciniae, small cone-shaped bodies, and the paired paraglossae, larger and thicker. That portion of the upper surface of the labium, which lies over the sub-mentum and mentum, is greatly swollen, and is produced forwards into a lobe which lies above the paraglossae and lacinae. This conspicuous
Fig 6.—Ventral view of cervical and thoracic regions.
1, 2, 3, Pro., Meso., and Meta-thorax; AB. 1 and 2, first and second abd. sterna; B. Eps., base overgrown episternum of prothorax; Cx., Coxa; EPM., epimeron; EPS., episternum; F.S., furcasternite; LCS., lat. cerv. sclerites; Oc., occiput; PCP., pleural coxal process; PN., pronotum; P.S., prosternite; PRC., precoxale; PFS., postfurcasternite; Rim., rim at margin occipital foramen; Sp. 1 and 2 thor. spiracles; SPS, spinasternite; Tr., trochantin; VCS., vent. cerv. sclerites? VS., verastenite.
structure is the hypopharynx. It is soft and spongy, and on each side is strengthened by a chitinous framework. Beneath the forwardly produced lobe is the opening of the salivary duct.
There are two pairs of lateral cervical sclerites (Fig. 6). The anterior and smaller sclerite of a pair is articulated to the rim, forming the lateral margin of the occipital foramen, at the point where the rim is divided transversely into two by a slight invagination. The posterior and larger sclerite is separated from the anterior by a transverse invagination or apodeme. In the ventral surface of the neck are a pair of faintly chitinized small circular patches, forming a transverse row. These may represent ventral cervical sclerites.
Prothorax. (Fig. 6.) The pronotum is very broad from side to side and overlaps the insertions of the legs. Beneath its anterior margin the neck and posterior portion of the head can be withdrawn. The first thoracic spiracles are situated below its postero-lateral margins. According to Martin (1916) the sternum of Insects consists of five subdivisions. The prosternum of Hemideina appears to agree with Martin's typical sternum. Anteriorly is a small faintly chitinized area—probably the prosternite. Immediately behind this is the verasternite. At each anterior corner this is produced into a long arm, directed forwardly and laterally. Each arm appears to end just below the antero-lateral margin of the pronotum, but here it is really continuous with the episternum, which as usual in the propleural region of Orthoptera has been overgrown by the pronotum. These arms, then, connecting verasternite and episterna are the precoxal bridges or precoxales. The furcasternite is fused with the verasternite, but a transverse constriction is evident between them. This sternite bears the furca, which consists of two upright processes, each terminating in a thin forwardly directed plate. There is no postcoxale. The postfurcasternite is divided into two halves by a longitudinal non-chitinized area of membrane. The spinasternite is
small and oval, and bears the single median spina. Du Porte (1919) states that in Orthoptera the pro-pleural regions are not crowded out but are overgrown by the pronotum, and that overgrown propleura are general throughout Orthoptera (Fig. 7). He figures the propleura of various Orthoptera, including those of three Locustids. A very small portion of the episternum can be seen externally below the lateral margin of the pronotum in Hemideina. Within and just below the pronotum are two lateral flat plates, each extending from just below the lateral margin of the pronotum to about half way up to the mid-dorsal line. The anterior margin of each is slightly inflected and parallel with the posterior margin. The dorsal margin is rounded. The width of each plate is about one third that of the pronotum. Along the posterior margin of each plate is a thickening, which at its ventral end articulates with the coxa. The ventral margin of each plate is also thickened and the anterior end of this thickened ventral margin is curved inwards and articulates with the trochantin. This flat plate is really hollow, i.e. it is a flattened bag with sides closely apposed and opening by a mouth just below the lateral pronotal margin. In a softened skeleton a needle can be passed through the mouth into the bag. These structures then result from the overgrowth of the pronotum over the propleura. Each bag may be regarded as having two closely apposed sides, an outer and an inner. The inner side represents the episternum, its thickened posterior margin the entopleural ridge or pleural suture, the ventral articulation of this pleural suture with the coxa the pleural coxal process, while the epimeron is absent or represented by a minute portion of the plate posterior to the entopleural ridge at its dorsal end. In the Locustids described by Du Porte, conditions are very similar, the epimera being very reduced, while the episterna are large.
The outer side of the bag results, presumably, from overgrowth of the pronotum over the propleuron. Moreover this outer side is continuous with the pronotum. For diagrammatic clearness we may compare the crayfish thorax in transverse section. The gill-chamber would represent the cavity of the bag, the thoracic side-wall the pleuron (episternum here), the branchiostegite the overgrown pronotum. The bag-like structure is a natural consequence of the overgrowth. The trochantin, a small triangular sclerite, articulates with the coxa at the middle of the latter's anterior margin and also with the anterior end of the thickened ventral margin of the episternum.
Mesothorax. (Fig. 6.) The mesonotum is broad from side to side, but not so broad as the pronotum. Its anterior margin is inflected and overlapped by the pronotum. In the mesosternum only three sternites can be made out. Verasternite and furcasternite are fused, forming one large plate whose posterior margin carries the medifurca. Extending from the antero-lateral margin of this sclerite to the base of the episternum is on each side a small transverse sclerite, probably the precoxale. It is separated by membrane from both sternum and episternum. The medifurca consists of two diverging arms with expanded extremities, each of which articulates with the pleural arm of the pleural suture of its side. Immediately behind fused verasternite and furcasternite is the small spinasternite carrying
the T-shaped spina. The mesopleura consist each of an anterior episternum and a posterior epimeron, separated by the pleural suture, which is not quite vertical but directed obliquely backwards. The pleural suture projects inwards as the pleural ridge or entopleuron. Its ventral end articulates with the coxa as the pleural coxal process, just above this is the prominent pleural arm or process which rests against or articulates with an arm of the medifurca. The trochantin, a transversely placed triangular sclerite, articulates with a small process on the antero-mesal margin of the coxa, while at its other end it abuts against the base of the episternum. The second thoracic spiracle is situated below and slightly behind the epimeron.
Metathorax: The metanotum is overlapped anteriorly by the mesonotum. The metasternum consists of a large verasternite to the candal margin of which the small furcasternite is fused. The metafurca consists of a median basal process giving off two laterally diverging processes. Each of these at its extremity bears three processes, the middle one of which is large and articulates with the pleural arm of the pleural suture. There is no separate spina. Episternum and epimeron are present on each side separated by the oblique pleural suture, as in the mesothorax. Pleural arm for articulation with the metafurca and pleural coxal process are present. In both meso-and meta-thorax the pleural suture runs from beneath the antero-lateral corner of the meso- or meta-notum, as the case may be, obliquely downwards and backwards to the pleural coxal process. The trochantin articulates with a process on the antero-mesal margin of the coxa and extends from this process to the base of the episternum.
Legs. The legs consist of the usual joints—coxa, trochanter, femur, tibia, and tarsus. The tarsus is four-jointed, the proximal segment or basitarsus is longer than the next two and carries two euplantulae or pads. The next two segments are short, each carrying a pad. The distitarsus is long, is provided with a median, elongated pad, and carries a pair of terminal ungues or claws. Ventrally, between ungues and distitarsus is a plate, the unguitractor, which retracts the claws when it itself is pulled back by a tendon. In the prothoracic legs the coxa bears a large outwardly-directed spine. Crampton (1923) states, “The trochanter articulates with the coxa but does not articulate with the femur in any insect I have examined, and it is quite possible that the trochanter may be a constricted off portion of the femur.” In the metathoracic legs of Hemideina the trochanter is firmly attached to the femur, there being no articulation between them. But in the prothoracic and mesothoracic legs there is a small but distinct articulation between trochanter and femur. In the prothoracic tibiae are the paired auditory organs. On the anterior and posterior surface of each tibia is a depressed oval area, the tympanum. On the posterior surface of each metathoracic femur, near the trochanter, is an area bearing numerous minute spines. When the hind-legs are raised and brought down against the side of the body, the spiny area on the femur rubs against a file on the second abdominal segment, the spiny area and the file thus forming a stridulating organ. The disposition of the spines on the legs is given by Hutton (1896) in his description of the species.
Abdomen. The terga cover the dorsal and lateral aspects of the abdomen. They are connected to the sterna by membraneous areas in which are the spiracles, and also small faintly chitinized plates representing lateral elements. The first abdominal sternum is small, and is separated on each side by the insertion of the metathoracic leg from its tergum. The second abdominal tergum bears on each side the file for the stridulating organ. A single sur-anal and paired par-anal plates surround the anus. They are large and distinct.
In the abdomen of the male there are ten distinct terga. Between the tenth tergum and the par-anal plate of each side, is a cercus, consisting of a small basal segment (basipodite) and a long cigar-shaped segment. There are nine sterna. The ninth sternum forms the hypandrium. It is large, undivided and bears a pair of styli on its caudal margin. The male genitalia will be discussed under the reproductive system.
In the female there are also ten terga, and a pair of cerci, each cercus consisting of two segments, as in the male. There are eight sterna, the eighth forming the sub-genital plate.
Fig. 8.—Dorsal view of ovispositor with parts separated.
Cerc., Cercus with basipodite at base; DP., member of dorsal pair; IP., member of inner pair; VP., member of ventral pair; LS., lat. sclerite; PP., par-anal plate; SP., sur.-anal plate; 9 and 10, ninth and tenth abd. terga.
The ovipositor (Fig. 8) is long and slightly curved. It is composed of six pieces in three pairs,—a dorsal pair, a ventral pair and an inner pair, (1) Between the members of the dorsal pair, near their bases, a dorsal transverse bar extends, and this bar has a small back-wardly-directed median process. At the base of each member of this pair is a small sclerite situated laterally. This sclerite appears to
belong to the ninth abdominal segment. Ventrally each member is connected to its fellow by a transverse bar with which the members of the inner pair are also connected. (2) The members of the ventral pair articulate with the small lateral sclerites of the ninth abdominal segment (?) already mentioned. (3) The inner pair is the smallest. Its members are connected by a dorsal transverse hoop, which has a forwardly-directed median process. Their bases are connected to a ventral transverse bar, to which the members of the dorsal pair are also connected as mentioned above.
The bases of the dorsal and inner pairs are connected together for some distance and those of the inner pair much swollen.
Fig. 9.—Dissection of male to show alimentary and reproductive systems.
I, II, and III, thoracic segments; Cerc., cercus with basipodite at base; CR, crop.; COL, colon; GI, gizzard; IL, ileum; MAL, Malpighian tubules; MC, mesenteric caecum; MES., mesenteron; OES, oesophagus; PP., par anal plates; RE., rectum; SP., sur-anal plate; Tes., testis; TUB., larger tubules of vesicula; Ves., vesicula covered by smaller tubules; VD., vas deferens.
The Alimentary System.
This system consists of the alimentary canal with its glandular and excretory appendages.
A The Alimentary Canal. (Fig. 9.) This is roughly about twice the length of the body. Its divisions and their respective lengths are indicated below.
[The section below cannot be correctly rendered as it contains complex formatting. See the image of the page for a more accurate rendering.]
|Oesophagus and crop||2.4 cm.|
|Length of Insect||4.8 cm.|
The mouth is bounded above by the labrum, laterally by the mandibles and first maxillae and below by the hypopharynx. It opens into the oesophagus, a narrow tube which first runs upwards and then backwards below the brain and above the tentorial plate, leaving the head by the occipital foramen. The oesophagus swells into the very large crop, which fills the thorax and part of the abdomen. When empty, or only partially full, its surface is thrown into folds. Sections (Fig. 10) show that the wall of the crop consists internally of a thick layer of chitin and in this layer faint stratification-lines are visible. Below this layer of chitin is the chitin-secreting epithelium, resting upon a basement-membrane and with cell-boundaries not clearly defined. There are two muscular coats—an internal coat of longitudinal striated muscle-fibres and an external coat of circular striated muscle-fibres. From this circular muscular layer, muscle-fibres at intervals pass inwards through the longitudinal muscle-bundles and end at the basement-membrane. At its posterior end the
Fig. 10.—T.S. of wall of crop.
CH., chitinous intima; CM., circ. muscle; EP., epithelium; LM., long muscle; TR., trachea.
crop narrows considerably and its internal chitinous lining is raised into six longitudinal folds upon which are small teeth. This narrow passage leads into the gizzard (Fig. 11). Within the gizzard the six folds become large and prominent, each fold bearing about twenty large transverse triangularly-shaped teeth (primary teeth) whose bilobed apices project into the lumen. Each longitudinal row of primary teeth is flanked on either side by a row of smaller or secondary
teeth, there being, consequently two rows of secondary teeth between any two rows of primary teeth. Between any two adjacent rows of secondary teeth, at the bottoms of the channels formed between them is a longitudinal chitinous ridge not divided into teeth.
Fig. 11.—T.S. of wall of gizzard.
CH., chitinous layer; CM., circ. muscle; EP., epithelium; LM., long muscles imbedded in connective tissue layer; LR., long, chitinous ridge; PT., primary tooth; ST., secondary tooth; TR., trachea.
Thus in the gizzard there are six rows of primary teeth, twelve rows of secondary teeth, and six ridges not divided into teeth. At the posterior end of the gizzard the teeth suddenly cease, but the six folds are continued on without the teeth and project a very short distance into the mesenteron, when they also abruptly end. The toothless portion of four of these folds is grooved. These four in the natural position of the parts, are the two lateral pairs. The dorsal fold and the ventral fold each bears a flap-valve, which, when not in use, projects backward, parallel to the wall of the mesenteron, but which can be closed. In the closed position, the distal edges of the two flapvalves overlap, and a transverse partition between gizzard and mesenteron is formed. When the valves are closed, the only means of communication between gizzard and mesenteron is by means of the four grooves mentioned above. The chitinous layer is quite flexible between the teeth, but very dense, thick, and dark coloured where it forms the teeth or ridges. It is produced also into many hairs. The teeth are hollow, but their cavities are practically filled by epithelial, connective tissue, and longitudinal muscle-layers. The epithelium, as in the crop, consists of a single layer of cells in which cell-boundaries are hard to distinguish. It lies immediately below the chitinous layer, and in sections often appears many layered, but this is due to the fact that the teeth are frequently cut tangentially. Below the epithelium is a layer of connective tissue, very obvious in the primary teeth. The layer of striped longitudinal muscle projects, like the epithelium, almost to the tip of each primary tooth. It does not enter the secondary teeth or ridges. In the primary teeth the longitudinal
muscle-layer is imbedded in the connective tissue-layer, in which also tracheae ramify. The circular layer of striated muscle is enormously thickened.
The mesenteron is produced, at its anterior end, into two forwardly directed caeca, which lie, in the natural position of the parts, one dorsal and one ventral to the gizzard. Two muscular-layers are present in the mesenteric wall—an external layer of longitudinal muscle-fibres and an internal layer of circular muscle-fibres, the latter being striated, the former non-striated. Inside the muscular layer is a layer of connective tissue, and this is not simply a flat layer lying below the epithelium, but from it arise trabeculae which project into
Fig. 12.—Portion of mesenteric wall in L.S. showing six “pits.”
CT., connective tissue layer with trabeculae; CM., circ. muscle; LM., long muscle; SH., striated hem.
Fig. 13—Portion of mesenteric wall in T.S. probably about end of active phase.
CON., contents in lumen; CM., circ. muscle; EP., epithelium; LM., long muscle; PM., peritrophic membranes; R., region between epithelium and peritrophic membranes occupied by cast off digestive cellules, glo bules of secretion, etc.; SH., striated hem.
Fig. 14.—LS at junction of midgut and hindgut passing through a urinary bladder or ampulla.
AM., ampulla; CON., food contents in lumen; CM., circ. muscle; EP., mesenteric epithelium; EPL., epithelium of ileum; LM., long muscle; M., malpighian tubules; PM., peritrophic membranes.
the epithelium in an orderly fashion, in such a way that if we could view the connective tissue layer from its internal surface, we should see a honeycombed structure, which we do see in tangential sections of the mesenteric wall. The result of this structure is that in transverse or longitudinal sections we see trabeculae from the connective tissue-layer, projecting at regular intervals into the epithelium (Fig. 12). Each cell of the honeycomb may be referred to as a pit, and a pit in transverse section is generally four or five sided. At the bottom of a pit is a nest of small cells, which multiply by division. Snodgrass (1910) states that in the honey-bee he has not been able to find any of these cells actually in the process of division; and Cameron (1912) writing of the stick-insect says he has not observed any mitotic figures in them. Though not abundant, mitotic figures can be clearly seen in these cells in Hemideina. As a result of such division, some of the products of division are pushed up the side-walls of the pits and on to the lips of the pits, where of course they meet cells similarly formed from adjacent pits. From the bottom of the pit to its opening there is an appearance, so to speak, of a succession of cells continually clambering up the side-walls of the pit to the lips. As the diameter of the pits is only small and cells are forced up from below on all sides, these forced-up cells form a coherent layer about and above the mouths of the pits. The free surfaces of these cells, bounding the lumen of the midgut, bear a continuous and obvious striated hem. In a cross section of the midgut (Fig. 13) numerous concentric peritrophic membranes may be seen between the food-contents and the epithelium. According to Imms (1925) “the results of recent research indicate that it (the peritrophic membrane) is continually secreted by a band of deeply-staining gland-like cells situated at the point of junction of the fore and mid intestine (vide Gehuchten, 1890, Vignon, 1901, Bordas and others).” Further on, he says, “In the hive bee (Snodgrass), the larva of Aeschna (Voinov) and certain other insects a peritrophic membrane is described as being formed by the delamination of the inner or free margin of the cells lining the mid intestine.” In Hemideina the peritrophic membrane is formed as it is in the latter case i.e. from the free surface of the cells lining the mid-intestine. It appears to be formed at the base of the striated hem, i.e. at the surface of the epithelial cells. When the epithelium enters upon a stage of activity, probably the striated hem together with the peritrophic membrane, which in section appears as a fine line between the striated hem and the surfaces of the cells, is cast off. The striated hem seems to disintegrate, while the peritrophic membrane persists as such. Then follows an eruption of the epithelium, the cells about and above the lips of the pits being cast out into the lumen of the midgut, though still separated from the contents by the peritrophic membrane. It is surmised that these cast-off cells are filled with the digestive secretion. The epithelium must then be regenerated from the nests of cells at the bottoms of the pits and a new striated hem formed. However, large areas of these digestive cellules often appear to be cast off at a time when striated hem, peritrophic membrane to-be, and the digestive cellules, can be seen as a coherent mass in the lumen.
At the junction of mid-intestine and hind-intestine are six bladders or ampullae, disposed in a circle around the intestine and opening into it. Into each bladder opens a bunch of Malpighian tubules. The bladders open into the intestine by passages which separate the epithelia of mid-intestine and hind-intestine (Fig. 14).
The Ileum (Fig. 15) is short, but is as thick as the mesenteron. The chitinous cuticle is comparatively thin, much thinner, for
Fig. 15.—T.S. of Ileum.
CH., chitinous intima; EP., epithelium below which is a layer of connective tissue; CM., circ. muscle; LM., long muscle.
instance, than that of the crop. The epithelium, which consists of columnar cells, is often thrown into longitudinal folds, but is capable of being extended. Below the epithelium is a thin layer of connective tissue in which tracheae ramify. There is a circular layer of striated muscle, outside which are six longitudinal bands of striated muscle. From these latter, at intervals, fibres or groups or fibres pierce the circular muscular layer and run for some distance in the longitudinal epithelial folds, ending at the layer of connective tissue, so that in a cross-section three muscular layers may appear an internal longitudinal, a circular and an external longitudinal.
The Colon (Fig. 16) is long, bent upon itself, and about twice the diameter of the ileum. Its internal surface is raised up into numerous leaf-like or tag-like processes. These are large and visible to the naked eye at the anterior end of the colon, but diminish in size towards the posterior end. The processes are restricted to six longitudinal areas, from which they spread out among the contents of the colon. In a freshly-killed insect, if the colon be opened, the processes are not obvious at first, being imbedded in the contents of the colon. But if the colon be soaked in water, the contents can soon be brushed away and the tag-like processes exposed. Each process consists of a double layer of small epithelial cells. Between the six longitudinal areas carrying these processes are six longitudinal bands of columnar epithelial cells continuous with the smaller epithelial cells of the leaf like processes. The cuticle of the epithelium is thin. Below the epithelium is a delicate layer of connective tissue. There is a thin
circular layer of striated muscle and within this appear a few longitudinal bundles. Outside are six longitudinal bundles of muscle fibres as in the ileum.
The Rectum. A slight constriction separates the colon from the rectum. In the rectum (Fig. 17) the six longitudinal areas which
Fig. 16.—T.S. of Colon.
CH., chitinous intima; EP., epithelium; CM., circ. muscle; LM., long muscle; TP., tag-like processes.
in the colon bore the tag-like processes, persist as narrow corrugated areas, the corrugations appearing in cross-section. The cuticula covering the corrugated areas is moderately thick. Between the corrugated areas are to be seen the six longitudinal bands of taller epithelial cells, supporting a comparatively thin cuticula. These bands of taller epithelial cells are more extensive in the rectum than in the colon. They do not offer any appearance of glandular structure, though they agree with the description by Chun of rectal glands in Locusta viridissima (quoted by Packard, 1903). Minot has stated that Chun's description is applicable to the Acridiidae he has investigated, and he states that the rectal folds “do not offer the least appearance of gladular structure.” In Hemideina, beneath the portions of corrugated cuticula, a distinct epithelium is present. This is an answer to the challenge given by the figures of transverse sections of the rectum of the cockroach (Miall and Denny, 1886) and of the stick-insect, Bacillus Rossii (Cameron, 1912). In both these cases, the areas
Fig. 17.—T.S. of Rectum.
CM., circ. muscle; COR., corrugated areas, with thicker cuticula; LM., long muscle.
of corrugated cuticula are figured without any underlying epithelium. Miall and Denny state that in these areas the chitinous lining blends with the basement membrane, while Cameron says that between each two bands is a non-epitheliated interspace where the chitinous intima becomes corrugated and is closely applied to the basement membrane. No explanation of this anomaly is offered.
A thin layer of connective tissue is present beneath the epithelium and outside the connective tissue layer is a thin layer of circular striated muscle. Externally the six longitudinal bands, present in the ileum and the colon, are to be found here also. These six longitudinal muscular bands are attached to the body-wall between the ninth and tenth abdominal terga.
B. Glandular and Excretory Appendages of the Alimentary Canal.
The Salivary Glands. (Fig. 18.) There is one pair of diffuse salivary glands. They lie in the thorax below and at the sides of the crop. Each gland consists of a number of lobules, each lobule provided with a ductule. The ductules on each side unite, forming a main duct and the two main ducts themselves unite into a single duct, which opens to the exterior immediately below the hypopharynx and above the labium. Into the main duct of each gland opens a salivary reservoir. The main ducts and their branches are provided with taenidia, but not the reservoirs.
The Mesenteric Caeca. These two caeca lie, as already mentioned, one above and one below the gizzard. The epithelial layer is deeply folded, the folds projecting into the lumen, and both muscular layers are striated, otherwise they resemble the mesenteron. The caeca generally contain a dark brown secretion, which appears to be passed forwards into the crop.
Malpighian Tubules. There are about two hundred Malpighian tubules in the weta. They are long thin tubules, arranged in six bunches, each bunch opening into one of the six bladders or ampullae mentioned above. In a just-killed insect dissected in normal saline solution, a slow serpentine movement of the individual tubules is observable. Each tubule is accompanied by a small trachea. In a cross-section of a tubule (Fig. 19) externally is to be seen a delicate
nucleated membrane, the peritoneal membrane, the nuclei being rare and small. Inside this is a layer of large epithelial cells resting upon a basement membrane and with prominent nuclei. The internal margins of these cells, lining the lumen of the tubule, present a striated appearance, which is said by some to be due to the presence of numerous minute pore-canals.
The dorsal vessel or heart (Fig. 20) is a long delicate tube extending from the posterior end of the abdomen into the prothorax, from whence it is continued as the aorta into the head. The heart contains eleven chambers, marked off from each other by constrictions, and each chamber is provided with a laterally-placed pair of ostia. The eleventh or last chamber is smaller than the others, and its osta terminal and dorsally placed. The ostia appear as vertical slits with lips reflected inwards. They are not situated at the constrictions between chambers as is apparently usual, but at about the centre of the chambers. At the anterior end of the heart is an aortic valve. This consists of about twelve annular fibres close together. The extension forwards of the heart beyond this point constitutes the aorta. It is not chambered, and has no ostia. It bends ventrally, and opens between the paired oesophageal sympathetic ganglia in the head.
Fig. 21.—T.S., through heart region. DIA., diaphragm; HY., two-layered hypodermis, resting on basement membrane, chitinous cuticula not shown; HT., heart, the section passes through a pair of ostia; NPH., nephrocytes; TR., trachea.
The wall of the heart (Fig. 21) consists of a cytoplasmic layer containing nuclei and exhibiting a delicate transverse striation in sections. This layer is bounded internally by a very delicate membrane, and externally by a coarser membrane. Small tracheae are attached to the heart-wall, and the heart itself is suspended in position by delicate threads or filaments passing to the abdominal terga. The pulsating heart may be observed if an insect be decapitated, the dorsal body-wall removed, and pinned down in salt solution.
The heart is enclosed in a space, the pericardial sinus, bounded dorsally by the terga and ventrally by the diaphragm. The latter is a thin transparent nucleated membrane with numerous fine interlacing fibres running in it. Portions of it can be removed and examined, when it is seen to be perforated by numerous apertures,
generally small and oval in shape. Eleven pairs of alary muscles are present. They consist of striated fibres, and members of a pair take their origin dorso-laterally from the terga as narrow bands which then spread out fanwise upon the diaphragm. Within the pericardial sinus, on each side of the heart, is a mass of light-brown tissue. This consists of fairly large cells, not closely packed, often arranged in linear series, and mostly binucleate. The binucleate condition is obvious in fresh cells appropriately examined, though it is, of course, not always so obvious in sections. These are the pericardial cells or nephrocytes, said to have the property of storing up substances of an excretory nature. Above these cells, and above the heart also, are the dorsal tracheae.
Above these tracheae is the hypodermis which is here two-layered and rests upon a basement membrane. The upper layer contains numerous small nuclei, the cell boundaries not being clearly defined, and much pigment. The details of this layer are often obscured by the abundant pigment. The lower layer consists of large cells with large nuclei and abundant granular cytoplasm. They are usually elongated in a transverse direction. A rather similar state of affairs is described and figured by Berlese (1909, p. 470) for Periplaneta.
A few Malpighian tubules penetrate the diaphragm, a portion of their length thus lying in the pericardial sinus. The dorsal tracheae are also contained in the pericardial sinus.
In the thorax a ventral diaphragm is present. It lies above the salivary glands, which generally adhere to its lower surface. Associated with it are some ventral nephrocytes, binucleate as are the dorsal ones. The ventral diaphragm is thin and transparent, and I have been unable to make it out in the abdomen, if it is present. In the ventral region of the abdominal cavity the fat body-layer is very abundant. The blood is colourless and contains nucleated corpuscles. These are of two chief kinds—approximately circular and with granular contents, or spindle-shaped and with comparatively clear protoplasm. To obtain the blood, the best way is to cut off the top of the head. In doing so the aorta is cut and a plentiful supply may be obtained.
The brain or cerebral ganglion (Fig. 22) is placed above the oesophagus, the latter resting upon the tentorial plate. It consists of two pear-shaped masses, united above in their broader parts, the stalks diverging below, encircling the oesophagus and tentorial plate as the para-oesophageal connectives and joining the sub-oesophageal ganglion below. From the upper portion of the brain (Protocerebrum) arise three ocellar nerves, one pair and a single median one, each passing to its respective ocellus. Laterally from the protocerebrum also arise the optic nerves. Distally each nerve swells into a ganglion and from this ganglion seven to eight short tracts pass to the compound eye. Below the protocerebrum is the deutocerebrum and from this arise the antennary nerves, each of which is double from its origin, and also a pair of very fine nerves, no doubt the tegumentary nerves. The third division of the brain is the tritocerebrum, but this is not obviously distinct externally. It consists of two
halves, each half lying towards the base of the pear, and thus widely separate from its fellow. The halves are joined, however, by the post-oesophageal commissure, passing below the oesophagus. From the tritocerebrum arise the para-oesophageal connectives which pass
Fig. 22.—Brain and sub-oesophageal ganglion viewed from before. ANT., antennary nerve; BR., brain; F., frontal ganglion; LA., nerve to labium; LF., labro-frontal nerve; MD., nerve to mandible; MX., nerve to maxilla; MOC., median ocellar nerve; OC., ocellar nerves; OG., optic ganglion; OP., optic nerve; PAR., para-oesophageal connective; R., recurrent nerve; SC., post-oes commissure; SUB., sub-oes ganglion; TEG., tegumentary nerves?
to the sub-oesophageal ganglion and also the labro-frontal nerves. Each labro-frontal nerve immediately divides into two, the outer branch passing to the labrum, the inner curving round and joining the frontal ganglion. The sub-oesophageal ganglion lies below the oesophagus and is connected to the brain by the para-oesophageal connectives. From it originate paired nerves supplying mandibles, maxillae, and labium, and also a pair of connectives which pass backwards between submentum and tentorial plate through the neck to the first thoracic ganglion. There are three thoracic and six abdominal ganglia connected as usual by paired longitudinal connectives (Fig. 23). From the sub-oesophageal to the third thoracic ganglion, between any two adjacent ganglia, is an extra pair of connectives, the members of which lie outside the stouter main connectives. From each thoracic ganglion several pairs of nerves arise, one large pair supplying the legs of the corresponding segment. The first three abdominal ganglia are close together, the fourth and fifth further apart, and the fifth and sixth closer again. From the first abdominal ganglion arise two pairs of nerves, from the second to the fifth one pair each, while the sixth is the largest abdominal ganglion and gives off numerous nerves, supplying among others the cerci, the ovipositor in the female and the vesiculae seminales in the male. The visceral or sympathetic nervous-system is well developed. It consists of oesophageal sympathetic and ventral sympathetic systems. In the
oesophageal system (Fig. 24) we note a small frontal ganglion lying on the oesophagus a short distance in front of the brain. From it come off four nerves, anteriorly a frontal nerve to the labrum, laterally a pair of nerves which connect with the trito-cerebrum, and posteriorly a median recurrent nerve which runs back along the oesophagus and below the brain and then swells into a hypocerebral ganglion. The hypocerebral ganglion is hidden from view by a pair of oesophageal ganglia which lie over it. These can be separated, when the hypocerebral ganglion is exposed and is seen to be connected with each oesophageal ganglion. The oesophageal ganglia are also
Fig. 24.—Plan of oesophageal sympathetic system viewed from above. BR., brain; ANT., antennary nerve; CP., corpus allatum; F., frontal ganglion; H., hypocerebral ganglion; L., nerves to labrum; N., nerves to stomachic ganglia; OP., optic nerve; OES., oesophageal sympathetic ganglion; R., recurrent nerve.
connected with the brain. From the posterior margin of the hypocerebral ganglion arises a pair of nerves, each member of which runs along the side of the crop, giving off fine branches as it goes, and at the junction of crop and gizzard swells into a ganglion, the stomachic ganglion, from which numerous nerves passing to crop and gizzard arise. Behind each oesophageal ganglion and connected with it by a fine nerve is a small white flattened body, oval in outline, the corpus allatum. According to Imms (1925) the corpora allata, frequently mistaken for posterior oesophageal ganglia, are found in all orders of insects, and are to be regarded as ductless glands which secrete certain substances into the blood.
The ventral sympathetic system lies just above the ventral nervecord. Its constituent nerves are fine and delicate. Between sub-
oesophageal and first thoracic ganglia runs a median cord, which at the middle of its length is double for a short distance. Each half of this doubled part has a small ganglion from which several nerves arise. From the first thoracic ganglion arise a pair of nerves which run outwards to the first thoracic spiracles. Of the nerves arising from the second and third thoracic ganglia, each swells into a small ganglion and from these ganglia nerves run outwards to the second thoracic and first abdominal spiracles respectively. From the abdominal nerve cord arise seven pairs of sympathetic nerves. Each pair arises from a minute ganglion connected by a median nerve with the abdominal ganglion in front of it.
The sympathetic nerves run outwards and at some distance from the ventral nerve-cord junction with the peripheral nerves from the abdominal ganglia and from this junction branches arise, and by certain of these branches the spiracles are supplied.
The Compound Eyes and Ocelli.
The compound eyes are situated above and to the outer side of the antennae. Each projects considerably from the surface of the head-capsule, and each is surrounded by a thick chitinous ring, the ocular sclerite (Fig. 25). The eye, viewed from the exterior, looks dark in colour except that at the inner and dorsal corner of each eye is a small white triangular area. When the insect is in a horizontal position, these white areas look upwards towards the sky. The ommatidia below such a white area possess practically no pigment or very little indeed. They are easily distinguishable in a section from the
Fig. 25.—Part of head of male viewed from before to show compound eye and ocelli. ANT., antenna; ANT.S., ant. sclerite; C.E., compound eye; LOC., lat. ocellus; MOC., med. ocellus; OC.S., ocular sclerite; R., ridge upon which epicranial suture divides; W., white area on comp. eye.
Fig. 26.—T.S. through the two lateral ocelli. HYP., hypodermis; OC., ocellus; OCN., ocellar nerve. The cuticle has been removed, the rhabdoms are black.
remaining ommatidia by their clear appearance. Over this area also the corneal lenses differ from the remainder. The eyes are of the eucone type with the nuclei of the cone-cells located in front of the cone. A corneal lens or facet is slightly biconvex and consists of outer and inner layers of which the outer stains much more deeply than the inner. Below the lens would normally appear the corneagen cells, but these I have been unable to detect. Then appear four cone-cells which secrete the crystalline cone. The nuclei of the cone-cells are obvious, and are placed in front of the cone, while the cone itself shows a division into four constituent parts. The proximal portion of the cone is gripped by the four expanded distal ends of the rhabdom. These four soon unite into a single rod, and this apparently single rod extends to the basement membrane. The rhabdom is surrounded by the retinula cells which have produced it. They contain pigment. Their number was not accurately determined but appears to be seven. Around each ommatidium is a number of accessory pigment-cells, isolating it from its neighbours. The ommatidia rest upon a fenestrate membrane, through which nerve-fibres from the retinula cells pass.
Hutton (1896) in his description of the genus Hemideina mentions the ocellus as obsolete. In H. thoracica there are, however, three ocelli, and as these all show the typical ocellar structure (retinula cells, rhabdoms, etc.) we may infer that they are all functional. The ocelli are arranged in a triangle (Fig. 25), the two lateral ocelli being situated one on each side of a median ridge upon which the epicranial suture divides, while the median ocellus forms the apex of the triangle. The median ocellus looks forward while the lateral ocelli looks sideways. In section (Fig. 26) the rhabdoms are cut at all angles, and so a very irregular arrangement is presented. Here and there is seen a triradiate rhabdom surrounded by three retinula cells with nuclei. This structure I take to be a cross section, the retinula cells apparently being grouped in threes and producing the triradiate rhabdom. It is difficult to imagine all the structures seen in a section as fitting in with this conception, but it is the only regular arrangement I have been able to observe.
Before each ocellus, the hypodermal cells, in this region normally quite tall, become very short and small.
Only the briefest account of this system is given. It is remarkable for the number of dilated tracheae which it contains. These all possess taenidia, in shape resemble a straight sausage with ends passing into very narrow tracheal tubes, and may be referred to as tracheal sacs. Nearly all of them are superficially placed i.e. they occur just below the hypodermis and are surrounded by fat-tissue. The distribution of the tracheae and tracheal sacs was studied by an injection method described by Kirk (1924. Ten spiracles are present, two thoracic and eight abdominal, and there are two pairs of main
longitudinal tracheae, a dorsal pair and a ventral pair. It is intended at a later date to give an account of the distribution of the tracheae and the structure of the spiracles.
The fat-body consists of a densely white opaque tissue whose interwoven strands form a lace-like pattern. It is very abundant indeed, particularly in the ventral abdominal region, but it occurs in most parts of the body. It is a cellular tissue, the cells being large, nucleated, and four- to five-sided to rounded. In portions of it the cell boundaries appear to have broken down. Probably they do so in older specimens, as is said to be the case in the cockroach.
Male Reproductive System (Fig. 9).
The testes are two white bodies lying in the abdomen, one to each side of the alimentary canal. Each is roughly pear-shaped in outline, the broader end being that from which the vas deferens leaves. Each testis is made up of numerous elongated follicles, each follicle with a short efferent duct. The follicles are arranged at the periphery of the testis with their efferent ducts all leading into the central region of the testis, so that in a longitudinal section we see a central region packed with sections of ducts and a peripheral region of sections of follicles. The efferent ducts unite to form a single vas deferens which leaves the testis at its broader end. Each follicle is surrounded by a thin flattened peritoneal layer and this also serves, together with a thin layer of fat-tissue, to bind the various follicles together, so forming a testis. In a section of a follicle at its blind end can be seen several groups of spermatogonia, each group surrounded by a thin sheath or cyst, and along this thin sheath occur here and there cells, the nursecells. Such an envelope or cyst of nurse-cells is a spermatocyst. According to Miall and Denny, 1886 (note on p. 176), spermatocysts are peculiar to Insects and Amphibia. According to Berlese, 1909 (p. 924) the two kinds of elements, cyst or nurse-cells and germinative cells (spermatogonia) are differentiated at the blind end of the testicular lobule. Then a number of nurse-cells form a cyst around a number of spermatogonia. Berlese summarises the views of recent observers on the cyst-cell. The following is a free translation—“By Sutton (1900) and Voinov the cyst cell is compared to a primary spermatogonium, by Holmgren to an indifferent syncytium, by Paulmier (1899) and Gross (1904) to connective elements. Korschelt and Heider (1902) derive it from an indifferent initial cell. Finally Henneguy (1904) considers that the cyst cell ought to be homologised with the ovarian epithelial cell.”
Passing from the blind end of a follicle towards its efferent duct, the spermatocysts become larger, and their contents are at different stages in the process of spermatogenesis (primary and secondary spermatocysts etc.) until finally near the efferent duct the spermatocysts contain spermatids and spermatozoa. It should be noted here that the spermatids are quite free from one another. But in the vasa deferentia the spermatozoa are not free from one another. On the
contrary they are aggregated together in wisp-like groups or bundles (sperm bundles), and these sperm-bundles in the vas deferens are not enclosed in spermatocysts.
It seems clear from a study of sections that at about the junction of follicle and efferent duct the spermatocyst must break down, and at this time also all the spermatozoa in one spermatocyst become aggregated together to form a sperm-bundle. The sperm-bundles may be studied alive in teased preparations of the testes and vasa deferentia of the male and the spermatheca of the female. The sperm bundle (Fig. 27) is flat and asymmetrical and as it swims, rotates on its longitudinal axis. Seen on the flat, three areas are distinguishable in a bundle. The anterior part is a clear white area, convex anteriorly, the convexity, however, being nearer one side than the other, thus producing the asymmetrical appearance. On either side the clear white area is produced into a backwardly directed process. The middle part of the bundle consists of the massed heads of the spermatoza, the heads being inserted into and presumably bound together by the clear white area. Behind the heads is a narrow zone occupied by the middle pieces of the spermatoza, and then follow the tails. The tails are long and work in unison, propelling the bundle forwards. As to the formation of the sperm-bundle, before the spermatocyst breaks down, nurse-cells are seen within the spermatocyst. They perhaps have migrated inwards from the wall. Their nuclei are usually in process of fragmentation, and it seems possible that the cytoplasm of such cell or cells forms the clear white anterior end of the bundle into which the sperm-heads are inserted. The single spermatozoon exhibits an elongate head tapering to a fine point, a short middle piece and a tail about five times the length of the head.
The vasa deferentia are a pair of very closely coiled tubes which lead from the testes to the vesiculae siminales. The wall of the vas consists of externally a peritoneal coat and internally an epithelium lining the lumen.
The vesiculae are paired and the cavity of each is small. Externally a vesicula presents a bushy appearance. This is due to the fact that its surface is covered with very numerous diverticula, the accessory glands or tubules and these are of two kinds. Anteriorly is a bunch of larger tubules which open into the ventral surface of the vesicula, while the remainder of the surface of the vesicula is hidden from view by the very numerous smaller tubules. In sections streams of coagulated secretion can be seen pouring into the vesiculae from these tubules, and each vesicula may contain a mass of this coagulated secretion. In sections passing through the junction of vas deferens and vesicula, sperm-bundles can be seen entering the vesicula from the vas. Sperms are never, so far as I know, found in the tubules. The vesicula is lined by an epithelium continuous with that of the various tubules. Outside the epithelium is a thick layer of muscular tissue, which, of course, the tubules penetrate.
Posteriorly the veciculae unite in a very short passage which immediately opens into the ductus ejaculatorius. The ductus traverses a structure which I shall refer to as the penis. The ductus is lined by chitin, below which is a chitin-secreting epithelium, and outside this is a well-developed muscular layer of striated fibres. Within the ductus was foud on one occasion a mass, viscid in nature, and apparently nearly ready for expulsion. It was hardened (by reagents) and sectioned. It consisted undoubtedly of the secretion derived from the accessory glands or tubules, and within it were numerous spermbundles. It was evidently a spermatophore, but how the spermatophore
is transferred to the female I have been unable to observe. It is, however, the means of transferring a number of sperm-bundles to the female.
The sternum of the ninth abdominal segment is enlarged, forming the hypandrium (sub-genital plate). Terminally it bears a pair of small unjointed styli. Above the hypandrium is a large cavity, whose roof is formed partly by the ventral surfaces of the par-anal plates but chiefly by a membranous (i.e. not heavily chitinized) area of integument stretching cephalad from these. Its floor is formed by the upper surface of the hypandrium, also membranous. On each side, the membranous roof and floor meet, forming lateral walls. Posteriorly it opens to the exterior, but from the anterior wall of this cavity a single structure, the penis, projects caudad into the cavity, the membranous roof and floor being, of course, reflected on to the penis (Fig. 28). About the centre of the roof of this cavity are two minute pit-like depressions of the integument, which serve apparently only for the insertion of muscles. At each anterolateral corner of the roof is a small chitinous process to which muscles are attached. Perhaps these three structures represent the pseudosternite of other Orthoptera. According to E. M. Walker (1922), in Orthoptera the penis lies below the paraprocts and typically also under the cover of a projecting plate—the pseudosternite—which forms an arch over its base and serves for the origin of muscles. The arch may be prolonged into a pair of rami, partly encircling the penis at its base and inwardly forming endapophyses. Sometimes the endapophyses are separated from the pseudosternite and may be present in many (some Tettigonoidea) in which the pseudosternite has disappeared. This seems to be the case here—there is no pseudosternite, but the endapophyses remain.
The rectum, anal plates, and roof of the penis cavity may be removed and the penis observed. It is a single structure, wide and flattened dorso-ventrally. On its dorsal surface are two longitudinal grooves, so that it appears three lobed from above. The central lobe contains the ductus ejaculatorius, the thicker lateral lobes form its side-walls. The ductus opens at the end of the penis by a wide transverse mouth bounded by dorsal and ventral lips. The central lobe forms the dorsal lip. The ventral surface of the ductus is prominent and is deeply grooved in a longitudinal direction and its terminal portion forms the ventral lip. The penis is spinulose.
Female Reproductive System.
This system consists of a pair of ovaries, a pair of oviducts, a median vagina and an unpaired spermatheca. The ovaries (Fig. 29) in a mature female are large pear-shaped bodies situated in the abdomen at the sides of the alimentary canal. Each ovary consists of a number of ovarioles or egg tubes, there being about thirty-eight to forty ovarioles per ovary. What appears to be the lower third of an ovary is in reality an egg-calyx i.e. the upper much dilated end of an oviduct, which serves as a pouch for storing the eggs, and may hold eighteen to twenty eggs at once. The ovarioles of insects are of
two kinds—those with cells specialized to provide nutrition for the ova (meroistic) and those without such specialized cells (panoistic). In the latter case the follicular epithelium is believed to provide nourishment for the ova. In Hemideina and in Orthoptera generally there are no specialized nutritive cells. Following e.g. Imms, 1925, we recognise three regions in an ovariole (1) a terminal filament, a slender thread-like prolongation of the peritoneal layer. All the filaments of one ovary are bound together forming a common thread,
Fig. 29.—Female reproductive system. EC., egg calyx; OV., ovarioles; OVD., oviduct; SGP., subgenital plate; TF., terminal filament; VAG, vagina with aperture.
which is inserted far forwards into the pericardial diaphragm; (2) the germarium, the region below the terminal filament which appears as a mass of nuclei. From this region are differentiated the ova and the cells of the follicular epithelium; (3) the vitellarium—the main portion of the ovariole. This region contains a linear series of ova gradually increasing in size as they near the egg-calyx. Each ovum is surrounded by its own coat of follicular epithelium. The nuclei of these cells show various stages of amitotic division. Amitosis is known to occur in the follicular epithelium of the cockroach, cricket, and hog-louse, and is perhaps general in the follicular epithelium of Insecta. Each ovum consists of a mass of yolk with a large nucleus or germinal vesicle and a nucleolus or germinal spot.
The ovarioles of an ovary are bound together by a thin layer of connective tissue, and such a layer surrounds each ovariole. In this layer numerous tracheae ramify, arising from branches from the fifth, sixth, and seventh spiracles. Within this layer is the follicular epithelium, whose cells rest upon a basement membrane. This epithelium grows inwards between successive ova in such a way that each ovum is enclosed in a complete follicle or sac. Besides its nutritive function, this epithelium secretes on its inner surface the egg-shell or chorion. In a mature ovary the last ovum in an ovariole usually has a well-developed chorion and all the ova in the egg-calyx have one. The chorion is tough and strong,
and brown in colour. Its external surface is marked out into hexagonal areas, and in the centre of each is a cavity or canal, from which finer branching canals spread out deeper into the chorion. Spines arise from the network of broad ridges surrounding these cavities. Seen in section (Fig. 30) the chorion shows two regions. The endochorion consists of three dense parallel layers of chitin closely connected to one another by numerous trabeculae. The exochorion is the region nearer to the follicular epithelium and consists of a network of ridges surrounding the canals or cavities mentioned above. The micropylar area is situated at the anterior (cephalic) pole of the egg. The egg itself is elongate oval and about five to six millimetres long.
Fig. 30.—L.S. of portion of chorion of egg still in ovariole. CAN, canal with diverticula; EN., endochorion; EX., exochorion; SP., spine.
Fig. 31.—Spermatheca, side view.
Fig. 32.—T.S. of spermatheca. BM., basement membrane; CH., chitinous layer pierced by canals. Outside this are the two concentric circles of nuclei; MSC., muscular coat.
Fig. 33.—Small portion spermathecal. wall, highly magnified. BM., basement membrane; CA., chamber or dilatation at end canal; CH., chitinous layer lining lumen and pierced by canals. This figure slightly diagrammatic.
From the egg-calyx the oviduct of each side continues as a short narrow tube which unites with its fellow to form a short median vagina and this opens by a slit-like aperture upon the upper surface of the sub-genital plate. The sub-genital plate is connected to the seventh sternum by an articular membrane and can move up and down, its posterior margin being free.
The spermatheca (Fig. 31) is a median blind tube whose distal end is bent upon itself. It is situated below the rectum, and its opening is on a triangular plate just above the opening of the vagina. In cross-section (Fig. 32) it is seen to be lined internally by a thick chitinous layer. Outside this are two concentric cellular layers, and then a basement membrane. Finally outside the basement membrane is a fairly thick coat of muscle-fibres, the fibres running in various directions. The chitinous layer is pierced by minute canals (Fig. 33), which at one end open into the lumen of the spermatheca, pass through the chitinous layer and the first cellular layer, well into the second, where each canal ends in a small chamber or swelling. Owing to their minuteness the canals are difficult to trace through their whole length, but their arrangement appears to be as above described. The internal cellular layer probably represents the chitin-secreting epithelium and the external a glandular layer, whose products, no doubt, are collected in the chambers or swellings and pass thence by the canals into the lumen of the spermatheca, where they serve to nourish the sperms.
Note on Development.
In one night late in April, 1925, a female in captivity laid twelve eggs, and the following night nine eggs. They were laid singly in damp sawdust about half an inch below the surface. Six of these hatched out early in December of same year, so that the embryonic development in this case took about seven months. The first instar is shown in Fig. 3.
Berlese, A., 1909. Gli Insetti. Milano. Vol. 1.
Brunner, —, 1888. Monog. d. Stenop. und Gryll. in Verh. k. k. Zool und Bot. Gesellsch., Wien, vol. 38.
Buller, W., 1867. The Zoologist, vol. 2, p. 850.
Buller, W., 1870. Trans. N.Z. Inst,. vol. 3, p. 34.
Cameron, A. E., 1912. Structure of the Alimentary Canal of the Stick-Insect, Bacillus Rossii. Proceedings of the Zoological Society of London.
Comstock, J. H. and Kochi C., 1902. The Skeleton of the Head of Insects, American Naturalist, Vol. 36, No. 421.
Crampton, G. C., 1920. Terminal abdominal structures of Male Insects. Can. Ento. Vol. 52, No. 8.
Crampton, G. C., 1923. Preliminary Note on Terminology applied to parts of an Insect's leg. Can Ento. Vol. 55, No. 6.
Du Porte, E. M., 1919. Propleura and Pronotal Sulci of Orthoptera. Can. Ento., Vol. 51, Nos. 6 and 7.
Florence, Laura, 1921. The Hog Louse, Haematopinus Suis Linná; Its Biology, Anatomy and Histology. Cornell University, Agricultural Experiment Station, Memoir 51.
Fulton, B. B., 1915. The Tree Crickets of New York. N.Y. Agric. Expt. Station—Tech. Bulletin No. 42.
Hewitt, C. G., 1907. The Anatomy of the House Fly, Musca domestica. Q. J. Micro. Sc., Vol. 51.
Hudson, G. V., 1892. Manual of New Zealand Entomology, London.
Hutton, F. W., 1896. The Stenopelmatidae of New Zealand. Trans. N.Z. Inst., Vol. 29.
Imms, A. D., 1925. Text Book of Entomology, London.
Kirk, H. B., 1924. A method of injecting the tracheae of Insects. Trans. N.Z. Inst., Vol. 55.
Kirby, W. F., 1906. Synonymic Catalogue of Orthoptera, Vol 2, Part 1, London.
Martin, J. F., 1916. Thoracic and Cervical Sclerites of Insects. Ann Ento. Soc. Am. Vol. 9, No. 1.
Melin, D., 1923. Contributions to the knowledge of the Biology, Metamorphosis and Distribution of the Swedish Asilids. Zoologiska Bidrag. Band 8.
Miall and Denny, 1886. The Cockroach. London.
Pavlovsky and Zarin, 1922. On the structure of the Alimentary Canal and its ferments in the Bee. Q. J. Micro Sc., Vol. 66, No. 263.
Packard, A. S., 1903. A Text Book of Entomology. New York.
Rily, Packard and Thomas, 1880–82. Third Report of the U.S. Entomological Commission.
Sharp, D., 1901. Cambridge Natural History, Vol. 5. London.
Siebold, C. Th. v., 1854. Anatomy of the Invertebrata, London.
Snodgrass, R. E., 1910. Anatomy of the Honey Bee, U.S. Dept. Agric., Washington.
Tepper, J. G. O., 1892. The Gryllacridae and Stenopelmatidae of Australia. Trans. Roy. Soc. S. Aust.
Tillyard, R. J., 1917. Biology of Dragon Flies. Cambridge Zoological Series.
Walker, F., 1869. Catalogue of Dermaptera Saltatoria in British Museum, Part 1. London.
Walker, E. M., 1922. Terminal Structures of Orthopteroid Insects, Pt. 2. Ann. Ento. Soc. Am., Vol. 15, No. 1.