Art VIII.—The Structure of Amphibola crenata Martyn.*
[Read before the Otago Institute, 9th October, 1917; received by Editor, 17th December, 1918; issued separately, 14th May, 1919.]
The shell of Amphibola was first brought to the notice of European naturalists by being collected during Cook's voyage to New Zealand in 1769, but the earliest account of the anatomy of Amphibola we owe to Quoy and Gaimard in 1832. The only other accounts we have are those of Captain Hutton in 1879 and 1882, and of Bouvier in 1892.†
Quoy and Gaimard (1832) described specimens collected in New Zealand during the expedition of the “Astrolabe.” They ascertained that it was a true pulmonate, and that it was hermaphrodite. They give excellent figures of the shell and operculum, but only one of the internal anatomy, and that is lacking considerably in detail; while their account of the anatomy is inaccurate in several points, and not sufficiently detailed.
Captain Hutton (1879) noted the two small triangular tentacles, and described the kidney and alimentary canal in greater detail than Quoy and Gaimard, though his description of the intestine is not quite correct. He also figured and described the nervous system and reproductive organs. In 1882 he published some further notes, wherein he corrects his former account of the radula and traces what he took for the “oviduct” from the hermaphrodite duct. Further mention of Hutton's work will be made throughout my account.
For a systematic diagnosis of the species reference should be made to Suter's Manual of New Zealand Mollusca (1913) and Atlas of Plates (1915).
[Footnote] * This paper formed the basis of a thesis for Honours in Zoology at the University of New Zealand, 1916.
[Footnote] † I have been unable to consult this memoir.
Although in the original thesis submitted to the University of New Zealand the histological structure of the various organs was discussed and illustrated, I have thought it advisable to omit these matters in the present paper.
I wish here to express my indebtedness to Professor Benham for his valuable suggestions and great help in preparing this paper for publication.
Amphibola crenata is a basommatophorous pulmonate gasteropod found living on mud-flats in sheltered bays, both in brackish and in salt water. It belongs to a series of pulmonates sometimes termed “gehydrophilous” (Cook, 1895, p. 18), in which, while the gill has been replaced by a “lung,” the animal has not become truly an inhabitant of fresh water. Amphibola and some other genera, such as Gadinia and Siphonaria, are “intermediate between essentially fresh-water and essentially marine species.”
The larger specimens of Amphibola are found quite close to the sea, the smaller ones farther up the mud-flat. They occur in enormous numbers on all the flats around the Otago Harbour, and, indeed, all along the coast of New Zealand. They are, of course, covered during high tide, but are exposed to view at low tide, so that the greater part of their life is passed out of water. Nevertheless, sufficient water is retained in the mantle-chamber to keep the tissues moist.
These animals are exceedingly sluggish. When they are in their natural surroundings one has to watch them very closely to see whether they are moving or not; but if they are placed in a little sea-water in a dish their method of locomotion is readily studied. When examined on the shore the only evidences of movement are the slow twirling of the shell as it is being drawn up to cover the slightly extended head and foot, the latter of which is concealed in the mud, and the furrow traced out on its path. The most striking feature of this movement is the very small part of the foot that is exposed at any one time. Its method of locomotion is as follows: A small portion of the anterior part of the foot is protruded, and this acts as a temporary anchor. The shell is then drawn up to cover the exposed part, and as it is twisted from left to right during the process it leaves a small part of the foot exposed on the left side and behind. The animal then glides slowly forward for a space without twisting the shell at all. The above process is repeated, the movement of the shell sometimes being from right to left. The shell is carried at an angle to the surface on which the animal is walking, the right side of the shell being raised a little from the mud, while the left side almost touches it. The animal is very sensitive, retracting into the shell at the slightest touch or at any disturbance of the water.
Fig. 1.—Amphibola crenata from below (natural size), as seen creeping up the side of a glass vessel of fresh water and thus exposing the whole of the foot. The two lappets of the head project only slightly in front of it. f, foot; h, head; m, mouth; s, shell.
Although air-breathing, Amphibola is able to live a considerable time immersed in water, either fresh or salt. If kept in a glass of fresh water the cover of which is sealed up it will live for a week; if completely
immersed in fresh water but not so sealed up it will live for a fortnight; if completely immersed in sea-water it will live a month; but if left without any water at all it does not live more than a day. Even when the tide is low there is always a certain amount of water left in the mud, so that these animals are not, in their native habitat, left absolutely dry.
As Suter gives a good technical description and figure of the shell it is unnecessary to deal with it here.
The animal is of small size and of a beautiful rich black colour.
The head is but slightly marked off from the foot, and is relatively of great breadth (fig. 2). Its anterior region is rather deeply excavated in the middle line so as to form a pair of lappets, one on each side of the mouth. Some distance from these are situated the pair of small, flat, triangular tentacles, which in the majority are so deeply pigmented that the minute eye is not readily seen, but in paler specimens the eye is recognized as an extremely small black dot of darker pigment close to the tip of the tentacle. Quoy and Gaimard, though mentioning the eyes, failed to note the tentacles. Hutton (1879), however, describes the latter, but states that the eye is at the base. This error is repeated, naturally, in Suter's Manual, but any one who examines the creature with sufficient care will be able to confirm my statement.*
Fig. 2.—Dorsal view of the animal removed from the shall (× 2). The foot is bent upon itself so that the ventral surface of its posterior region is seen in front of the head. Some of the interior organs are seen by transparency, e, eye; g, groove into which anus opens; gp, genital pore; gz, gizzard; int, intestine; ipl, inferior pallial lobe; k, kidney; m, mouth; me, collar; pa, pulmonary aperture; rl, right lappet of head; t, tentacle; vf, ventral surface of foot.
The foot is short, and almost circular in outline, as seen from below (fig. 1). In preserved specimens it is very much shrunken, but if examined when the animal is walking it will be seen that the foot is capable of being expanded until a narrow margin is visible beneath the shell all the way round except on the right side. The foot is separated from the head by a slight furrow; there is no distinction into pro-, meso-, and meta-podium, nor have I found any trace of a pedal gland. The anterior part of the creeping-sole is cream-coloured, the posterior part greyish-blue.
[Footnote] * It is not surprising that the tentacles were overlooked by the earlier zoologists, if they had only preserved specimens at their disposal, for when the head is contracted they are difficult to distinguish from wrinklings of the body-wall. As to the eye, in ordinary specimens they, too, are indistinguishable in such material: it is only in fresh specimens and in those in which the pigmentation at the tip of the tentacles is less than usual that they can be seen. [W. B. B.]
Attached to the dorsal surface of the hind end of the foot is the operculum, closely underlying the shell so as to be visible only from the side. When the animal is completely retracted it fits close against the entrance to the spiral portion of the shell, and is firmly held there by muscles.
This characteristic prosobranchiate structure is found in this genus only amongst the Pulmonata.
The thickened edge of the mantle, which, of course, is fused with the neck, and which is usually called the “collar” (fig. 2, mc), is light in colour, and is very muscular. It does not project beyond the shell during locomotion, but if the animal is allowed to remain in fresh water the head becomes expanded and the mantle-edge appears under the outer lip of the shell. The upper lip of the pulmonary aperture is then seen fitting into the sinus of the shell.
The margin of the pulmonary aperture is not a simple circular aperture as in Helix, but the lower lip is produced outwards into an “inferior pallial lobe” (ipl) such as occurs in Chilina according to Lang (1900). This lobe is deeply grooved, the groove being triangular in shape, with the apex directed backwards towards the pallial chamber (fig. 2, g). The anus is situated at the apex of this groove. Hutton (1879) describes and figures the anus as being to the right of the pulmonary aperture, and both Hutton and Quoy and Gaimard draw the triangular furrow mentioned above as if it were part of the rectum. The anus is really posterior to the pulmonary aperture, although it is capable of being carried beyond it by the extension of the inferior pallial lobe. When the faeces are passed to the exterior the lips of the triangular groove probably close together, so that it is temporarily converted into a tube. This prevents any faeces entering the mantle-cavity. The inferior pallial lobe is also capable of closing against the upper lip of the pulmonary aperture.
Organs of the Pallial Complex. (Fig. 3.)
The most conspicuous organ on the roof of the mantle-chamber is the kidney, which presents several remarkable features. It is pure-white in colour, and occupies the middle region of the mantle, across which it extends obliquely for about two-thirds of its breadth: somewhat flaskshaped in outline, its apex is situated a short distance from the pulmonary aperture, its broader base close to the left side of the roof of the mantlecavity. Running along its ventral surface is a narrow band of muscle (mu) which arises from the middle of the hinder edge of the columella-muscle, which is not shown in the figure. The portions of the kidney on either side of this band are of unequal sizes.
The excretory aperture is a conspicuous longitudinal slit on a papilla at its anterior end (ex), which projects freely from the mantle itself. The wall of the kidney is thick, and internally bears numerous filiform papillae which almost fill its cavity. The excretory products can be seen by teasing up a portion and examining it in the fresh state: they appear as clear spherical vesicles of different sizes, each of which has a very thin envelope of a protoplasmic nature, surrounding a drop of hyaline, non-granular fluid. In the centre of this are several round concretions of a brownish colour.
Since the cells of the kidney are not ciliated, they will be unable to aid in the removal of excretory products. Probably the muscle-band which
runs along the dorsal surface of the kidney serves this purpose, by compressing the flow and so driving the stuff forwards to the pore.
Lying on the roof of the mantle-cavity, close to the anterior end of the kidney, and extending a short distance underneath it, is an oval mass of white rounded particles covered by a thin pigmented membrane (hy). It is situated in a curious depression which extends from the anterior end of
Fig. 3.—General dissection (× 2). The mantle, which has been cut along the collar and along the right side, has been turned to the animal's left, exposing the pallial complex. The head and neck have been opened to disclose the alimentary tract and part of the genital system. The rectal sinus has been severed at the point se, where it passes on to the roof of the mantle-chamber, ag, albumen-gland; as, anterior sinus; c, crop; cc, cut edge of collar; cd, common genital duct; ce, cut edge of mantle; d, depression in front of renal pore; dgl, digestive gland; div, diverticulum of oesophagus; ex, excretory pore; g, groove into which anus opens; gp, genital pore; gz, gizzard; hgl, hermaphrodite gland; hy, hypobranchial gland; irs, inferior rectal sinus; int, intestine; k, kidney; l, lung; Id, duct of digestive gland; m, mouth; mc, collar; mu, muscle-band on kidney; os, osphradium; pa, pulmonary aperture; pe, penis; pr, prostate; pv, pulmonary vein; r, rectum; se, cut end of rectal sinus; sg, salivary gland; srs, superior rectal sinus; st, stomach; t, tentacle.
the kidney to the edge of the mantle above the pulmonary aperture. When these particles are disturbed with a brush they give off a bluish fluorescent foam, which quickly re-forms as often as it is brushed away. When examined under the microscope the mass is seen to be made up of rounded particles of different sizes, which contain crowds of small granules. Though white by reflected light, the particles are brown by transmitted
light, and this colour is due to these granules, which are yellowish-brown in colour. They look like droplets of fat. Possibly this structure represents the hypobranchial gland, which, as Lang mentions, is absent in all pulmonates except Amphibola. This peculiar and striking phenomenon was met with in every specimen examined.
The heart lies at the base of the left side of the kidney: its wall is formed of a thin, but tough, transparent membrane. The auricle is much smaller than the ventricle, and broader posteriorly than at its anterior end. Its wall is very thin, white, and but feebly muscular. The ventricle is yellow in colour, and its wall is more muscular than that of the auricle.
The lung (l) is situated between the kidney and the anterior muscular edge of the mantle (fig. 3). The blood-vessels traversing it are not clearly visible, on account of the fact that they have very large cavities and extremely thin walls. Owing to the small size and very delicate walls of the auricle I was unable to inject the lung through the auricle, but I succeeded in injecting it through the pedal sinus, as will be described in the account of the circulatory system.
It is probable that dermal respiration plays as important a part as lung respiration, and the thick layer of pigment covering the mantle in the region of the lung may act as a respiratory pigment, as may also the pigment covering the other parts of the body.
Alimentary System. (Fig. 3.)
The mouth (m) is placed between the two lappets of the head, and opens into the cavity of the buccal mass. It is dark in colour, somewhat ovoid in shape, the posterior portion being swollen. From the ventral surface of this posterior portion the radula-sac extends backwards for a short distance below the oesophagus. There is no jaw, nor did I find any trace
of a rudiment of one. Two similar and symmetrical muscular masses project into the cavity of the buccal mass in front of the radula, one on each side of the middle line. They are dark in colour, and each is simply a muscular thickening of the wall of its respective side.
The radula is spatulate in shape, the pointed end being anterior. There are forty-four rows of teeth, the rows being set obliquely to the median
line. If the radula is mounted whole, only two kinds of teeth are visible, as it is very difficult to spread it out flat, but if separated with needles three distinct kinds can be distinguished (fig. 4)—(1) central, (2) lateral, (3) marginal.
The central tooth (tc) has a broad base, bearing a median cusp which is almost square in outline. On either side of this are a number of smaller cusps, six or seven, but the number differs with each central tooth and often on the two sides. The cusps next to the median on either side are smaller than those more remote; but all taper to a sharp point. On either side of the central tooth, and placed slightly above its upper margin, is a small elongated lateral tooth (il) which is somewhat blunt at the tip. Next to this is another lateral tooth, of larger size, which bears two cusps. The division into cusps is not the same in every tooth. Some have a large outer cusp and a very small, narrow inner one; in others the cusps are of equal length and breadth. But this difference is due probably to some being more worn away than others. The remaining teeth on each side of the laterals are the marginals (tm). They are all curved, simple, conical teeth, the tips of which are somewhat rounded.
Hutton (1879) describes only two kinds of teeth in the radula of Amphibola—median and lateral. He also says the spcies of the teeth point forward. He gives a very rough sketch of the radula, but the shape is not correct. In his second paper (1882) he redescribes the teeth. He notes that the median tooth has five or six cusps on either side, not two or three as he formerly thought; that there is a single lateral tooth, which is often divided into two and varies in shape; and that the rest of the teeth are aculeate, and increase in length towards the margin.
The form and great size of the median tooth in Amphibola seems unusual among pulmonates, for, judging from figures of radulas of other pulmonates (Bronn's Thierreich, pl. xcv)—e.g., Siphonaria, Limnaea, Planorbis, Auricula—the median tooth is much smaller and simpler than those on either side.
Perrier (1897) says that the form of the lingual teeth is related to diet: that they are obtuse and generally numerous in herbivorous molluscs, but have the form of a hook and are less numerous in carnivorous genera. The teeth in Amphibola, therefore, agree with those of other herbivorous molluscs.
A pair of salivary glands open into the buccal cavity (fig. 3, sg) near the commencement of the oesophagus. Each gland is a long, linear, yellow, sacculated structure, which passes through the nerve-collar and runs for a short distance backward beside the oesophagus. Posteriorly they taper, and are attached together and to the wall of the oesophagus.
The oesophagus extends backwards for about two-thirds the length of the body. The posterior portion lies beneath the intestinal coil, and is visible by transparency on the ventral surface of the uninjured animal. As far as the intestinal coil the oesophagus is a narrow tube, but it then dilates a little, the dilatation being marked off from the portion in front and behind it by constrictions. This specialized portion of the oesophagus is the crop (c). Behind the crop the oesophagus becomes broader, and on a level with the posterior end of the intestinal coil it bears a finger-shaped diverticulum on the right side (div). Behind this diverticulum the oesophagus becomes broader, and opens into the stomach (st), which is U-shaped, the right limb being much smaller and narrower than the left, which extends forwards towards the heart. An outgrowth of the left limb of the
stomach forms the gizzard (gz), which consists of two globular and symmetrical muscular projections separated by a muscular girdle. If the stomach be opened and its wall examined, two folds of the epithelium in the form of a pad will be seen on its floor, one behind the entrance to the gizzard and the other just in front of it. From each of these two pads a white wavy fold runs along the floor of the stomach towards the intestine. Another wavy fold is present to the right of these two.
The stomach passes into the intestine (int), which, after running underneath the aorta on the left side of the body, crosses the median line and then forms the intestinal coil. The intestine is very long, measuring in some specimens 8 ½ in. when uncoiled. It is coiled round and round the albumengland (ag) in a double spiral, the total number of complete coils being eight, only five of which are visible on the surface. It coils four times from right to left, the fourth coil crossing the middle of the albumen-gland transversely. After coiling four times in the opposite direction it runs along the right side of the first coil and passes into the rectum. The coils from left to right alternate with those from right to left. The rectum (r) runs along the right side of the body, and opens by the anus into the triangular groove already mentioned.
The extremely long coiled intestine is characteristic of herbivorous gasteropods. Amphibola has to pass through its alimentary canal enormous quantities of mud in order to obtain the vegetable matter it requires. Examination of the contents of the stomach and the mud itself shows that the food consists principally of diatoms. Several different kinds were found, the most frequent being Navicula. The faeces are deposited in long circular strings.
Hutton's drawing (1879) of the gizzard and stomach is not quite correct; and he says there are only five coils in the intestine, all reversed. He draws the triangular groove into which the anus opens as if it formed part of the wall of the rectum itself.
The digestive gland (fig. 3, dgl) is very large, occupying together with the gonad the hinder end of the body, and extending from the region of the stomach up to the apex of the visceral spire. It occupies the median portion of the spire, and lobes extend to the edge alternating with those of the gonad. It is a much-lobed gland, dark brown in colour, and when examined fresh it is seen to be dotted with numerous brown specks, the so-called entochlorophyll granules.
The duct of the liver, which appears to be single, opens into the right limb of the stomach, near its anterior end (ld).
The cells lining the lumen of the liver are long columnar cells, but they are of varying lengths, some extending a considerable distance into the cavity, others being very short. Two kinds of cells are distinguishable. (a.) Liver cells: The large cells mentioned above, as well as smaller liver cells, contain small granules, which give the yellowish-green colour to the fresh liver. They stain pink in eosin. (b.) Ferment cells: These occur in amongst the liver cells, and each has a large cavity containing a yellowish-brown granule. These entochlorophyll granules can be seen at various stages of formation, some cells containing minute granules, others granules a little larger, others again very large granules. I tried several tests for these granules, with the following results: They turned red when treated with gentian violet, turned pale green when treated with methyl green, remained brown when treated with osmic acid, and turned dark green when treated with eosin. Acetic acid had no effect; but they dissolved in caustic potash.
These entochlorophyll granules are just as numerous in a fasting animal as in one that has been feeding. The only difference I found was that the granules from a fasting animal dissolved in caustic potash at once; those in the other animals took a long time, some of them not dissolving at all.
Schneider (1902) distinguishes three kinds of cells in the liver: (a) liver cells, (b) excretory cells, (c) lime cells.
According to him, two sorts of granules occur in the “liver cells”—small liver-granules, which stain red in eosin, and large excretion granules (entochlorophyll). The “liver cells,” he says, perform a nutritive and secretory function. The “excretory cells,” he says, stain a deep black in osmic acid. The “lime cells” contain phosphate of lime.
The liver cells, as I have described, are present in the liver of Amphibola. I tested for “excretory cells” with osmic acid, but obtained no result; and of “lime cells” I could find no trace.
MacMunn (1900) regards the cells containing entochlorophyll in molluscs as “ferment cells.” He also describes “lime cells,” but finds no trace of the so-called “excretory cells.” He tested for glycogen in the liver, but obtained no results. Nor have I found any trace of glycogen in these cells in Amphibola.
The Nervous System. (Fig. 5.)
The nervous system consists of a ring of nerve-tissue surrounding the buccal mass a short distance from its posterior end. The ganglia are bright-orange in colour.
The cerebral ganglia are connected by a fairly stout cerebral commissure. From each there passes backwards and downwards a slender connective to the buccal ganglia, which are, as usual, of small size, and are situated slightly behind the entrance of the salivary gland. From the buccal ganglia, which are joined by the commissure, small nerves are given off to the buccal mass.
From each cerebral ganglion the following five nerves are given off to the anterior region of the head: (a) A very fine nerve, which runs alongside and close to the buccal mass, innervates the head lappet in the region of the mouth; (b) to the outer side of this is a nerve which almost at once bifurcates; (c) a very fine nerve, and (d) a stouter one which bifurcates (these two run parallel with the posterior branch of nerve b); (e) the two tentacular nerves run outwards and slightly upwards to enter the base of each tentacle, and one of the two innervates the eye.
From the right ganglion there also arises a stout nerve (f) which runs outwards and backwards and then bifurcates, the two branches supplying respectively the anterior and posterior portions of the penis. There is no corresponding nerve on the left side of the animal.
The pleural ganglia lie on the body-wall close to the cerebral, to which each is connected by the cerebro-pleural connective. There are apparently no nerves given off by these ganglia, but from the right pleuro-pedal connective, and nearer to the pedal than to the pleural ganglion, a slender nerve is given off which bifurcates almost immediately; the anterior branch (g), crossing below the penis, goes to the anterior end of the common genital duct, the posterior supplies the body-wall. On the left side the corresponding nerve, which also bifurcates, is, of course, entirely limited to innervating the body-wall of this side.
The pedal ganglia are of about the same size as the cerebral; the pleuro-pedal connectives are very short. From the pedal ganglia several large nerves supply all regions of the foot.
The only really interesting feature about the system relates to the character of the visceral loop, which is much longer in Amphibola than in ordinary pulmonates. From the right and left pleural ganglia a connective passes back to the visceral ganglion (gv), which is situated on the bodywall below the oesophagus, slightly to the right side. It is about the same size as one of the pedal ganglia, and, as we shall see later, probably represents the fused infra-intestinal and abdominal ganglia. From it are given off two strong nerves. The anterior one (k) runs out to the right side, ventral to the common genital duct, and bifurcates, one branch running up to supply the inferior pallial lobe, and the other backwards alongside the rectum. The posterior nerve (l) is stout, and runs backwards to supply the organs in the visceral spire.
Fig. 5.—The nervous system in situ (× 4). a, first cephalic nerve; d, fourth cephalic nerve; f, penial nerve; g, nerve of genital duct and body-wall; h, nerve to osphradial ganglion (which is represented in outline as it lies on the roof); j, nerve to body-wall; k, rectal nerve and its branch to the inferior pallial lobe; l, visceral nerves; m, n, nerves to body-wall; cd, common genital duct; ce, cut edge of mantle; gac, accessory ganglion; gos, osphradial ganglion; gsi, supra-intestinal ganglion; gv. visceral ganglion; pe, penis; r, rectum; t, tentacle.
A short distance from the pleural ganglia the visceral commissure bears two ganglia asymmetrically placed, the one on the right (gsi being larger and farther removed from the pleural ganglion than the one on the left (gac). The right one may be termed the supra-intestinal, and from it are given off two nerves.
The osphradial nerve (h) runs outwards to the osphradial ganglion, which is situated on the mantle on the right side. The osphradial ganglion itself gives off small nerves to the osphradium and the mantle. A slender nerve (j) supplies the body-wall.
The ganglion on the left is evidently an accessory ganglion (gac) which corresponds to that found on the visceral commissure in Chilina (Lang, 1900, p. 220; and Naef, 1911). This accessory ganglion sends off a nerve (n) which supplies the body-wall in the region of the collar.
Between this accessory ganglion and the visceral ganglion, but nearer the latter, a nerve (m) arises from the visceral commissure and supplies the columellar muscle. There is no ganglion corresponding to this nerve, though perhaps it arises from cells in the accessory ganglion.
According to Pelseneer (1906), “In all Euthyneura except Actaeon, Chilina, and Latia the infra-intestinal ganglion is fused with the abdominal in such a manner that the latter appears to participate in the innervation of the mantle—i.e., inferior pallial lobe.” Although we find that the inferior pallial lobe in Amphibola is innervated by a nerve from the visceral ganglion, yet serial sections across the latter give no indication of the union of two such ganglia.
In another primitive pulmonate, Latia, however, as figured by Pelseneer (1906) the approximation of the ganglionic centres has not gone so far, so that the infra-intestinal ganglion, although very close to the abdominal, has not fused with it. Latia, like Amphibola, has an accessory ganglion near the left pleural. The nervous system in Latia enables one to see how the condition in Amphibola may have come about.
The comparison of the nervous system of Limnaea, Chilina, and Amphibola will show more clearly that the visceral ganglion in the last probably represents the fused infra-intestinal and abdominal ganglia.
Hutton's description and figure of the nervous system do not agree with what I have found to be the case. He says that in addition to the cerebral and pedal ganglia there is “a parieto-splanchnic system, which consists of seven ganglia, three on each side, and an azygos infra-oesophageal ganglion connected with the others on either side.”
The anterior ganglion of his parieto-splanchnic system corresponds to the pleural ganglion; the posterior one to the accessory and supra-intestinal respectively; but I find no trace of the middle ganglion on either side. He observes no difference in size in these two ganglia, nor their asymmetry; nor does he mention any buccal ganglia. Nothing is said as to the various nerves themselves.
Sense Organs.—Tactile organs are distributed all over the surface of the head and foot. This is evident by the sensitiveness exhibited when the animal is touched, and also by the rich nerve-supply, especially in the anterior margin of the head.
A statocyst (or otocyst) is present on each pedal ganglion. It is an oval vesicle, and contains numerous calcareous lenticular statoliths. When examined fresh the statoliths oscillate in the fluid present in the vesicle. These movements cease after a short time. Some of the statoliths lie on the base of the nerve which leaves the statocyst. This nerve is seen running close against the cerebro-pleural connective, so that one may conclude that the nerve of the statocyst comes from the cerebral ganglion.
The osphradium is a simple epithelial ridge on the roof of the mantle-cavity close to the collar, near the pulmonary aperture (fig. 3, os). A nerve can be seen supplying it from the osphradial ganglion, which is in its turn innervated from the supra-intestinal ganglion. Hutton (1879) figures and describes the statocyst, but makes no mention of the osphradium.
The eye, as sections show, presents no peculiarity in structure; it is quite typically constructed. When a tentacle is mounted entire the eye
exhibits two distinct portions—a small linear light area, which represents the lens; and a deeply pigmented region, surrounding this but for its anterior end, is the retina (fig. 7). Below the eye, embedded in the substance of the tentacle, may be seen a mass of rounded particles of carbonate of lime such as occur throughout the tissues of the body.
Circulatory System. (Fig. 3.)
The only portion of the circulatory system that needs describing is the venous system. In order to trace out the veins I injected the animal through the foot. The best results were obtained with glycerine carmine, and the kidney was invariably well injected.
The blood is collected into sinuses, as can be proved by thus injecting the animal. From the larger sinuses the blood passes into two main tubular sinuses or veins, the anterior sinus and the rectal sinus (fig. 3).
On the left side the blood from the body enters the anterior sinus (as), which lies along the collar. Shortly before reaching the pulmonary aperture it curves round to connect with the pulmonary vein (pv), which runs close beside the kidney, to enter the anterior end of the auricle. The anterior sinus gives afferent branches to the lung (l) along its whole course, and the blood is collected by efferent branches which enter the pulmonary vein. Thus, though some of the blood enters the pulmonary vein directly from the anterior sinus, most of it reaches the heart only after filtering through the vessels of the mantle-roof, which constitutes the lung.
The rectal sinus consists of two superposed channels, one above the other—the inferior rectal sinus (irs) and the superior rectal sinus (srs). The inferior rectal sinus commences at the inferior pallial, lobe, and runs along the floor of the mantle on the right side of and close to the rectum. It extends back as far as the coils of the intestine, where it leaves the bodywall floor of the mantle-chamber and, bending abruptly on itself, passes forward along the roof of the mantle above its former course as the superior rectal sinus (srs) as far as the pulmonary aperture. It then bends at right angles and traverses the mantle as far as the commencement of the collar, where it seems to cease. The blood, which enters both ends of the rectal sinus, is carried through vessels traversing the mantle from the sinus to the afferent renal vein, which runs along the dorsal surface of the kidney, and which is therefore not shown in the drawing. The blood from the afferent renal vein is then distributed through the sinuses in the connective tissue which supports the filiform papillae of the kidney. These trabeculae of connective tissue are traversed by axial sinuses which function as blood-spaces. The blood thus reaches the efferent renal vein, which runs backwards near the ventral surface of the kidney, below the muscle-band, to enter the auricle.
I have had great difficulty in tracing out the circulatory system. The heart and blood-vessels have such extremely thin walls that it is impossible to inject them from the heart. On one occasion the injection went from the auricle along the pulmonary vein and into the anterior sinus directly for a short distance, but I did not observe any injection on the wall of the lung itself. By injecting through the foot the kidney was invariably well injected, and sections across the lung showed that the vessels of the lung had also been injected. As explained above, the afferent and efferent vessels on the wall of the lung are not as clearly visible in Amphibola as in Helix and in other pulmonates. The same is true of the vessels running
from the superior rectal sinus to the renal vein. Sections across the mantle between the kidney and the rectal sinus, however, show the existence of these blood-vessels.
The rectal sinus where it traverses the roof of the mantle is very conspicuous. Quoy and Gaimard (1832) draw it as if it were coming from the ventricle. Hutton (1879) says it does not come from the ventricle, as Quoy and Gaimard figure; but he was unable to trace its connection, nor does he seem to have traced out the circulatory system at all. When the animal is opened by cutting along the right side of the mantle the rectal sinus is necessarily cut across at its hinder end where it bends upwards on to the roof of the mantle. I am not quite certain whether the superior rectal sinus ends, as shown, near the collar (fig. 3), but I can trace it no farther.
Although the rectal sinus in Amphibola is a definite blood-vessel, I have called it a “sinus” in order to compare more easily the circulatory system with that of a typical pulmonate—e.g., Helix. The superior rectal sinus, then, evidently corresponds to the so-called rectal sinus of Helix, the inferior rectal sinus being an additional vessel. The circulation of blood in the lung and in the kidney agrees with that found in Helix, except that in Amphibola, as in other primitive forms, the blood after being purified in the kidney enters the heart directly.
Amphibola, like all the Euthyneura, is hermaphrodite. The genital organs lie for the most part on the right side of the body, and comprise the hermaphrodite gland (or ovotestis), albumen-gland, and an undivided genital duct, into which open certain accessory organs.
The genital aperture is situated at the base of the right tentacle (fig. 2), and presumably serves for the exit of both ova and spermatozoa, though I have been unable to trace the course taken by the ova in their passage to the exterior.
The ovotestis (hgl), together with the liver, occupies the visceral spire. On the ventral surface it is plainly seen as a light-yellowish-brown organ extending the whole length of the spire and embedded in the dark-brown gastric gland. On the dorsal surface, however, only portions of the gland are visible, separating the darker bands of the liver (fig. 3). It consists of several lobules, each composed of numerous acini, the ends of which are tipped with a dark-brown pigment. These lobules communicate with small ductules which unite to form the hermaphrodite duct (hd). Posteriorly it is of a rich brown tint, but anteriorly it becomes paler till it is white. This leaves the ovotestis as a very wavy duct, which passes forward on the ventral surface of the visceral spire to open into the common genital duct (cd). Just before the point of entrance it gives off a small finger-shaped diverticulum, the seminal vesicle (sv), which underlies the duct and rests close against the albumen-gland.
Pelseneer (1895) in a paper discussing the origin of hermaphroditism in the Mollusca refers to Amphibola in these terms: “The wall of the genital gland shows distinct sexual differences upon the two sides of the follicles, in which the female side exhibits projections which are rudiments of the acini of this sex.” It will be remembered that Cottrell (1911) shows that in Siphonaria the peripheral acini or follicles produce only eggs, whereas the central ones produce spermatozoa. In Helix each follicle produces both kinds of germ cell from any part of the epithelium. My own observations tend to show that Pelseneer's statement is correct, except that I do not find
any “projections” from the side of the follicles. Sections across the ovotestis of Amphibola show that ova and spermatozoa are developed in the same follicle. The spermatozoa, however, are confined to one portion of wall, while from the rest of the epithelium the ova are formed. They develop at a later period of the year. Spermatozoa are fully developed in November, whereas at this date the ova are still small and not ready to be discharged.
The common genital duct consists of two dictinct regions—(a) glandular, (b) non-glandular. The glandular region (gld), into which the hermaphrodite duct leads, lies in close contact with the posterior ventral portion of the
Fig. 6.—The genital system unravelled so as to exhibit as much as possible (× 2). The point of entrance of the prostate into the cavity of the penis is indicated by dotted lines. ag, albumengland; cd, common genital duct; gld, glandular portion of common duct; gp, genital pore; hd, hermaphrodite duct; hgl, hermaphrodite gland; pe, penis; pi, prostate; sv, seminal vesicle.
albumen-gland (ag). It is a white, mucilaginous, finely coiled tube, all the coils of which I have not attempted to show in the drawing. This tube gradually loses its mucilaginous character and widens to form the commencement of the non-glandular portion (cd), which narrows again as it passes forward along the body-wall parallel to, and on the left of, the rectum as a wavy duct of a cream colour. It reaches almost to the base of the right tentacle, narrowing slightly as it does so. It then turns sharply on itself, runs backwards, and after a short distance bends abruptly and becomes much enlarged to form the penis (pe), which is a pyriform organ of a light-cream colour with very muscular walls.
Opening into the common duct are two diverticula, the albumen-gland and the prostate. The albumen-gland (ag) opens into the distal end of the glandular region opposite the point at which it passes into the non-glandular. It is a brownish or orange-coloured tubule, which is very much convoluted, as Hutton described, and forms a spherical mass, around which are wound the numerous coils of the intestine. It is soft and of a somewhat slimy consistency, and its cells secrete a great quantity of mucilaginous material.
At the commencement of the penis is situated the prostate (pr). It is a much-convoluted blindly-ending tube, the distal half pure-white in colour, the proximal half bright-yellow. From this end a slender duct leads away, which, after running in the substances of the muscular wall of the penis, communicates with its cavity near its opening to the exterior.
From the above description it will be seen that the condition of the genital duct in Amphibola agrees with the most primitive condition in the Euthyneura—that is, the duct is a sperm-oviduct throughout its length. To this type of duct Lang (1900) and Pelseneer (1906) give the name “monaulic.”
As far as I can ascertain, the only other primitive pulmonate closely related to Amphibola which exhibits a monaulic type of duct is Siphonaria. Cottrell (1911) shows that the reproductive organs of this genus differ from those of Amphibola in three chief features: There is no separate albumen-gland, but the common duct is itself glandular, and the much-folded walls of this duct constitute the albumen-gland; the common duct enters the penis close to its external pore and not at its distal extremity; and there is a large spermatheca, the long duct of which opens into the penis close to the common duct. The absence in Amphibola of a distinct and definite spermatheca seems a peculiarity.
Limnaea, which has affinities with Amphibola, has a “diaulic” type of genital duct which cannot be compared with that of Amphibola. In Chilina, another primitive pulmonate, the reproductive system of which Lang (1900) figures and describes, the genital duct is “diaulic,” the openings of the sperm-duct and oviduct being at some distance from each other. Considering the close relationship of Amphibola and Chilina, one would have expected a greater similarity in their reproductive systems.
Quoy and Gaimard (1832) described the reproductive system of Amphibola. They called the hermaphrodite gland the “ovary,” and the hermaphrodite duct the “oviduct.” The albumen-gland they named “testicule,” and the genital duct which runs up on the right side the “uterus.” The opening of the female portion of the duct they figure on the right side of the body, to the left of the anus. The penis they describe as opening near the eye, in the place where the right tentacle would be if it were represented in the figure.
Hutton (1879) correctly describes the hermaphrodite gland and the hermaphrodite duct. The albumen-gland he says consists of two parts—an albumen-gland proper and an accessory gland. The albumen-gland proper opens into the hermaphrodite duct by a duct. According to him, the hermaphrodite duct appeared to divide beyond the albumen-gland into a large sacculated “oviduct,” and a narrower but still broad “vas deferens” (which is the “common duct” of my account), but he could not satisfy himself as to how the oviduct left the hermaphrodite duct. He describes it as running along the left of the rectum, to which it is firmly attached. “It appears to open inside the respiratory cavity,” but of this he
says he was by no means certain. In a later paper (1882) he says he found an animal with the oviduct distended with eggs, and it showed clearly that his supposed “accessory gland” was the commencement of the oviduct.
I can find no opening of a female duct in the position figured by Quoy and Gaimard, nor do I find any oviduct as described by Hutton. What he supposes to be the commencement of the oviduct is the lower end of the genital duct; and serial sections in this region prove this to be so.
Sections across the right side of the body show no trace of a duct between the rectum and the genital duct, whereas sections across the genital duct itself show the existence of a deep fold in its wall, which serves to divide the duct into two portions, presumably, during the passage of the ova and spermatozoa.
Hutton (1879) says the eggs of Amphibola are “lodged on the exterior of the mantle in a circular patch near the opening of the renal organ. After fertilization they acquire a thick coat which gives them a bluish-white pearly appearance.” These are evidently the fluorescent particles I described in connection with the kidney, where I mentioned that they were products of the hypobranchial gland. They are not eggs, as I have observed them in every animal without exception that I have examined during the year. Moreover, they do not resemble eggs in the slightest degree.
In his second article (1882) Hutton says he found the oviduct so distended with eggs that he was able to trace its connection with the hermaphrodite duct. The “eggs” he found in the oviduct were, I think, the eggs of a parasitic Trematode. I have found them several times, and in some animals they are so numerous on the right side in the muscular region of the body-wall between the rectum and the genital duct that both the rectum and the genital duct are hidden from view—i.e., in the position of Hutton's supposed “oviduct.”
At present I am making systematic observations on Amphibola so as to ascertain at what time the ova are laid and how they get to the exterior. Every month I collect and preserve the animals in order to cut sections of the reproductive organs and ascertain at what time of the year the eggs are laid. If successful I shall try to follow out-the development of the eggs as far as possible.
Fig. 7.—The end of a tentacle, with the eye, cleared and mounted entire, c, carbonate of lime; l, lens; p, pigment; t, tip of tentacle.
Embedded in the connective tissue and amongst muscles in all parts of the body are numerous bodies composed of carbonate of lime. They are extremely abundant, especially on the mantle-edge. They vary in size, the smallest ones being found embedded in the base of the tentacle below the eye (fig. 7). They vary in shape also, some being spherical, others
ovoid, and others again more or less rhomboidal. Examined under the high power some exhibit fine circular striations. When treated with acetic acid they dissolve, giving off large bubbles of carbon dioxide, which can be plainly seen with the naked eye.
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