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Volume 16, 1883
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Art. VI.—On the Anatomy of Sepioteuthis bilineata, Quoy and Gaimard.

[Read before the Wellington Philosophical Society, 31st October, 1883.]

Plates III.–VIII.

(Note.—Owing to my having been unable, until within the last week or two, to obtain large and perfect specimens, I have not, as a rule, introduced other than relative measurements. The drawings, except those from the microscope, are natural size; and with the exception of pls. v., vi., vii., fig. 1, and viii., figs. 5–9, are made from the specimen figured at pl. iii. I regret that I have been unable to replace all the drawings by those of large specimens. The largest specimen I have seen measures 14 inches along the posterior surface of the mantle, this length not including any portion of the fins. To avoid confusion of terms, I have described the animal as though it were in a walking position, head downwards; but have adopted the practice, sanctioned by Professors Nicholson and Huxley, of showing the drawings in the reverse position. The terms anterior and posterior are applied to the so-called “dorsal” and “ventral” surfaces respectively.)

The distribution of Sepioteuthis bilineata is given by Professor Hutton (Manual of N.Z. Mollusca, 1880) as from Wellington to Auckland. In Wellington Harbour it is tolerably abundant during late spring and summer; but, with the exception of a few small ones in July. I have never seen a specimen during the winter months. Professor Hutton points out that there is nothing in Dr. Gray's description of S. major that does not apply to this species. The habitat of S. major is given as Cape of Good Hope (Catalogue of Mollusca in the British Museum); but Dr. Gray's description is very brief. Moreover, he gives S. bilineata in his catalogue.

External Characters.

The body is elongated and somewhat cylindrical in shape, but is flattened on the posterior surface, and still more so on the anterior surface. Its widest part is immediately above the base of the mantle, thence it narrows regularly to its extremity, where it is rounded. The edge of the mantle forms a complete collar round the “neck.” On the anterior aspect of the animal the mantle-border is produced into a marked angle on the median line, this angle lodging the anterior extremity of the internal shell. From this point it recedes towards the posterior aspect, rising slightly on either side of the funnel, but immediately falling away in a well-defined curve at the base of the funnel. The two slight angles formed by the production of the posterior mantle-border mark the tips of the “articular” cartilages, adapted to fit into the “hinge” cartilages of the funnel.

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Fins.—The fins are large and thick. They are attached to the sides of the body near its anterior aspect, and start from the mantle-border or close to it. They at once begin to expand, and their outline forms a curve widest at about its middle. They extend somewhat beyond the extremity of the body and coalesce. Their margin becomes thin, and often allows the coloured dorsal integument to shine through its substance like a purple band. Below the dermal layer is a thick muscular coat, whose fine but well-marked fibres extend from the inner to the outer margin of the fin. At the widest part of the fin they are parallel, but on either side they begin to radiate towards the outer margin, this radiation being most marked on the upper side. As the extremity of the body is approached they become less noticeable, and immediately opposite the extremity are not generally observable. On both aspects of the fin they are usually visible through the epidermis, and where they are most marked can be distinctly felt with the finger.

On the anterior aspect of the body the line of union of the fins is distinctly visible, although the fins are so apparently a continuation of the mantle that there is no marked depression.

Head.—The head is broader than long, its greatest width being at the projecting eyeballs. Behind these it contracts to a kind of “neck,” similar to that noted by Professor Owen when speaking of Sepia palmata (Trans. Zool. Soc. of Lond., vol. xi., part 5). Below the eyes there is also a well-marked contraction at the base of the arms, though this contraction is not so striking as the upper one. The anterior surface of the head is flattened, and between the eyes is a depression which lodges the anterior production of the mantle-border when the neck is contracted. The posterior surface of the head is also flattened and has a marked depression which lodges the funnel. The eyes are on the sides of the head and are directed straight outwards. They present the character of the family in being covered with skin. When the tentacles are extended the sacs for their partial reception are easily discovered by pressure.

The ridge of integument (pl. iii. b) running behind the eye and parallel with its curve, and which Professor Owen in his description of S. brevis (Trans. Zool. Soc. of Lond., vol xi., part 5) regards as an external ear, is very well marked, amounting indeed to a groove covered by a fold of integument. This organ is, so far as I can discover, the same that is regarded by Professor Huxley Anatomy of Invertebrated Animals, 1877), and by Professor Macalister (Introduction to Animal Morphology, 1876), as olfactory in function. It is neither so large nor so striking as in Loligo vulgaris, figured in Professer Nicholson's Manual of Zoology, p. 428 of sixth edition.

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Funnel (pls. iii., iv. a, and viii., fig. 16).—The funnel is large, flattened, somewhat conical in shape, longer than broad, and rounded at its apex. On each side of its base is a cartilaginous expansion, presenting a groove to lodge the articular ridges developed on the inner surface of the mantle. Its margins lie loosely upon the funnel. Between the surface of the head and the funnel are muscular bands; and these are so strongly developed on either side as to form a cup-shaped cavity at the base of the funnel between it and the head.

Inside the aperture of the funnel is a strongly-marked infundibular valve (pl. viii., fig. 15 i), so placed that, when depressed, it entirely closes the aperture. Its free portion forms a semi-circular curve; but the lower part is attached by the margins, so that, when the free portion closes the aperture, the opening of the funnel leads into a blind cavity.

Arms (pls. iii., viii., figs. 5–8).—The fourth pair of arms is the longest; next in length is the third; next the second; the first being the shortest and slightest. The arms of the fourth pair are 4-angular in section, and present a slight groove on the peripheral surface, the groove being caused mainly by the great production of the anterior peripheral margin, which is continued below to form the outer wall of the tentacular sac. Those of the third pair are 3-angular, the peripheral surface presenting a sharp angle. The second pair are 3-angular or irregularly 4-angular; and the first have the peripheral surface rounded, or approach 3-angular.

The fourth and third arms on each side are connected by a peripheral web, which forms the outer wall of the tentacular sac. This web is attached to the inner peripheral margin of the fourth arm, and to the centre of the peripheral surface of the third arm. It extends to near the tip of the fourth arm, but only a short distance along the third. A very small web connects the third and second arms; and the second and first have a small web attached at the base to the peripheral surface of each. It extends a very short distance along the second arm, and a still shorter along the first.

The arms all taper to their extremity. There is a well-marked brachial membrane extending along each side of the acetubular surface of the arms and forming a fold, at whose base the suckers are inserted.

The suckers are arranged in alternate pairs, and this arrangement is observable from the point near the base of the arms at which they first begin to near the tapering extremity, where they become minute tubercles. Each sucker (pl. viii., figs. 10, 11) is sub-spherical or shortly cylindrical in shape, and is borne on a pedicel attached, not to the centre of the base of

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the sucker, but a little to one side. The margin of the sucker has a horny ring with small teeth more strongly marked on the higher than on the lower side. From the base of each pedicel a raised band runs across the brachial membrane to its edge.

Tentacles.—The tentacles vary in length relatively to the body, but when thrown back and fully extended often reach beyond its extremity. They are oval in section, except at the clavate portion where they are 3-angular. The suckers are similar to those on the arms, but are arranged in alternating rows of four, are larger and have the horny ring more strongly marked. A membrane, similar to that on the arms, is developed on each side of the acetabular surface.

Each tentacle has a muscular band attached for a short distance near its base and widening into a web which connects it with the inner wall of the tentacular sac. The sac is not large enough to receive more than a short portion of the tentacle, and probably contraction is limited to the extent of the muscular band.

Oral Surface.—The outer lip or buccal membrane (pl. iii. a) is a simple membrane with seven marked angles, showing the points of attachment of brachial frœna. The structure here is very similar indeed to that described by Professor Owen as occurring in Loligopsis ocellata (Trans. Zool. Soc. of London, vol. xi., pt. v.). Of the frœna, the first springs from the small basal web between the arms of the first pair; on each side of this is one springing from between the second and third arms; next one springing from the base of the acetabular surface of each third arm; then a similar one from each fourth arm. The surface of the buccal membrane is smooth.

The inner lip (pl. vii., fig. 1a.) is thick and muscular, and its border is marked by strong regular corrugations.

The whole surface of the head and body is richly spotted with chromatophores. They extend over the anterior surface of the fins, but only a short distance from the body on the posterior surface. They extend along the peripheral surface of the arms, and even along the surface of the first three brachial frœna. They occur sparingly on the acetabular surfaces of all the arms, and on the peripheral surface of the tentacles. There are none on the funnel.

Microscopic Structure of the Integument.

The chromatophores, when examined under the microscope, show, as prevailing colours, black or very deep brown, chocolate-brown, cloudy-purple, full pink, and pale yellow. Each chromatophore appears to have around it a few loose muscular fibres; and at times I have fancied I have detected a loose transparent capsule, with muscular fibres in its walls. In

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Sepioteuthis Bilineata.

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Sepioteuthis Bilineata.

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such cases the chromatophores are well-defined; but often the outline is very ill-defined in one direction. This may, however, be due to the coloured contents having flowed out, leaving a part of the capsule empty, its thin walls being often invisible from their transparency.

The chromatophores appear to be in two distinct layers, as at times one may be seen distinctly overlying another. Thus a deep brown chromatophore may be seen over a yellow one; pink may be seen over yellow; chocolate-brown over pink, and so on.

Above the layer or layers containing the chromatophores is a colourless cuticular layer; below it is a layer containing muscular fibres.

The whole integument is very loosely attached by fine muscular fibres to the substance of the animal; it is loose, but nowhere wrinkled, and is very elastic.

Cartilages.

The cartilages are—the cephalic cartilage, the neck cartilage, the hinge and articular cartilages, and the pinnal cartilages.

Cephalic cartilage (pl. viii., fig. 2).—The cephalic cartilage forms, when the animal is in a walking position, a roof for the eye-balls. An idea of its general shape may perhaps be best obtained by imagining a broadly cordate leaf with its apex and the base of the midrib infolded towards the centre. The posterior side shows a marked depression, and the outline is here strongly concave. From within the central point of the posterior margin rises a slight prominence, which gives off two small wing-like cartilaginous expansions which lie upon the eye-ball. The anterior outline is concave, as are to some extent the lateral margins. The cartilage is pierced at its centre by the aperture for the gullet and visceral nerve branches. This aperture has its margin strengthened by a cartilaginous ridge on either side, the two ridges receding slightly from the aperture, but becoming confluent on the posterior aspect and rising to form the prominence already noted. In the cup formed by the receding of these ridges lies the peri-œsophageal nerve ring. On either side of the ridge formed by their confluence are two perforations.

Neck cartilage (pl. viii., figs. 3, 4).—Lying on the neck is a cartilage of irregular diamond shape. Its sides are incurved, so as to give it a spoonshape. Attached to it, and passing upwards, is a double muscular band attached at its opposite extremity to a tough membrane which covers the gladius. Thus the neck of the animal is strongly attached to the anterior part of the mantle. The anterior aspect of the cartilage has a raised central ridge, grooved throughout its length. This ridge corresponds with the channel of the gladius.

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Hinge and articular cartilages (pl. iv., b, c).—The hinge cartilages are two developments, one on each side of the funnel. Part of the cartilage is free and expands slightly on the surface, having a longitudinal central groove. The portion that is imbedded in the substance of the funnel is triangular in section, the base being at the surface. This cartilage is long and narrow, and the ends of the surface-portion are rounded.

Corresponding with these hinge cartilages are two slightly raised cartilaginous ridges, one on each side of the inner posterior surface of the mantle. These cartilages are not so marked as those of S. brevis, Owen (Trans. Zool. Soc. of Lond., vol. xi., pt. v.). When the mantle is contracted they fit into the cartilaginous sockets on the funnel. They extend quite to the mantle-border, forming the angles that on the posterior surface give the appearance of shoulders. It is impossible to observe any definite outline in the imbedded portion; indeed it would seem that the ridges are rather hardened elevations of the mantle than true cartilages.

Pinnal cartilages.—A long cartilage, having a low thickened central ridge with thin dilatations on each side, extends the whole length of each fin. A section in the thickest part shows a low triangle, whose broad base lies against the body of the animal, and to whose sides the muscles of the fins are attached; but the outline is in most parts irregular.

A thin cartilaginous plate of oval outline lies at the base of the funnel.

Muscles.

On a dissection along the posterior surface being made, one of the most striking features are the musculi retractores infundibuli (pl. iv. a) extending from the base of the funnel to somewhat beyond the centre of the anterior surface of the mantle, where they are attached, one on each side of the gladius. In the groove between these elongated muscular masses lie the intestine and ink-sac, the penis and the œsophagus, with the mass of the liver.

The double muscular band already spoken of as being attached to the neck cartilage probably serves to change the position of the neck. The neck has also two well-marked muscular masses lying under the musculi retractores infundibuli.

Each arm shows a central mass of muscle-fibres channelled for blood-vessels and nerves. From this central mass radiating fibres are given off to a circular muscular coat lying beneath the surface of the arm.

Gladius (pl. viii., fig. 1).

The gladius is lanceolate in shape, and is transparent. The central rib is well marked, and has a deeply excavated channel. It extends beyond the dilated wings about one-sixth of the total length. The broadest part is

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at about three-fifths of the total distance from the apex, where the breadth is about one-tenth of the length. The gladius is lodged in the anterior aspect of the mantle; and the posterior wall of its chamber is formed by a tough transparent coat, whose consistency approaches that of cartilage where it covers the apex. The gladius extends the whole length of the mantle.

Circulatory and Respiratory Organs (pls. iv. and v.)

The systemic heart (pl. iv. i) lies about the centre of the pervisceral cavity. In shape it is nearly triangular, the base of the triangle lying towards the oral end of the body. The right side is the larger, owing to the great cephalic aorta being given off from this side. Lying at the base of the branchiæ are the large branchial hearts (pl. v., fig. 1f), globosely ovoid in shape, and with their axis forming an acute angle with that of the body. At its inner end each has a small fleshy appendage (pl. v., fig. 1f'), and each is encased in a chamber with transparent membranous walls (id., k).

As it approaches the heart the vena cava (id., b) divides, one branch going on each side of the intestine at its point of flexure and entering the branchial heart on its upper surface. Veins (pl. iv., v, v) are seen converging on the inner side of the mantle to enter the vena cava. These cross from the mantle by the peritoneal membrane which is thickened for the purpose. Similar veins run from the anterior aspect of the body, entering the vena cava with those from the sides of the mantle.

After passing from the branchial heart through the gills the blood enters the systemic heart at the two dilatations (“auricles”) already noted as giving the triangular shape to the heart. The left auricle is the more strongly marked, the right being somewhat obscured by the great development at the point whence the cephalic aorta (pl. v., 1 c) is given off. Shortly from its commencement this aorta gives off branches to the liver. At its opposite end the heart contracts to give off the posterior aorta (id., h), which, shortly after its commencement, divides into three branches, these being borne along reflexions of the peritoneal membrane to the mantle.

The branchiæ (pl. iv., g, g; pl. v., fig. 1) are large and prominent, the tip extending to beyond the base of the funnel. About 70 non-ciliated lamellæ are given off on each side. The continuation of the branch of the vena cava, after passing through the branchial heart, forms the central axis of the gill on the anterior side; and it is attached throughout the whole length of the gill by a suspensory membrane (id., a) to the anterior mantle surface. On the posterior side, the branchial vein forms the central axis. Each lamella is bordered by two capillaries, one running from each of the axes of the gill and meeting at the apex of the lamella, and themselves

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borne on a fine suspensory membrane. Across the space between them stretch still smaller plume-like lamellæ (id., fig. 2), each with a small capillary. These sub-lamellæ look like repetitions of the entire gill; but, on microscopic examination, it is seen that they consist of a capillary with a very thin membrane thrown into transverse folds (fig. 3) on each side.

The renal organ (fig. 1 g) is well-developed on the branches of the vena cava. Two long lobes extend over the heart, which they almost hide; and each of these lobes has a well-marked opening, which communicates with its branch of the vena cava. Thus, if air be blown into one of the openings, it inflates its branch of the vena cava, and also the branchial heart into which that branch opens.

Reproductive Organs.

Male (pl. vi.).—The male organs consist of a testis, vas deferens, “prostate” gland, duct of the “prostate,” receptacle of spermatophores and penis. The testis (fig. 1 g) lies at the ab-oral end of the body, is large, irregularly oval in outline, and flattened. Its lower outline is concave, its upper convex. It is encased in a thin membrane attached on its anterior surface and uniting it below with the inner anterior surface of the mantle.

The vas deferens communicates with the capsule of the testis towards the upper end. Its commencement seems rather to be lost in the membrane than to have a well-marked opening. It is short but slender, and does not present the convolutions noticed in all descriptions of the male organs of Cephalopods that I have seen.

The vas deferens opens into a long, cylindrical vesicula seminalis, which leads to the “prostate” gland. The walls of the vesicula present well-marked transverse plicæ. Except that it narrows at either end, it is of about the same thickness throughout. It contains spermatozoa, which appear, when examined with the ¼-in. objective, to be simple straight rods. Though the walls of the vesicula appear to be thick and white, they are in reality thin and transparent, the white colour being caused by the spermatozoa. The plicæ may possibly be due to only partial distention.

The “prostate” gland (fig. 1 d; fig. 2) is a delicate tube, presenting marked convolutions, and having the appearance, when viewed on the posterior aspect, of a spiral coil. At the point where the vesicula seminalis enters it is dilated (3); then there is a strong convolution; then a slightly expanding tubular portion (2), which leads to a sac-like portion (1). Near the point where the vesicula enters is a small cœcal dilatation (4); and a similar dilatation is produced from the saccular portion from which the duct springs.

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Sepioteuthis Bilineata.

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Sepioteuthis Bilineata.

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From the saccular portion, near the opening of this dilatation, springs the duct of the “prostate” (c). The wall of the “prostate” contains a network of branching and interlacing fibres.

The “prostate” gland differs from that of S. brevis, Owen, where it is described as an “oblong, blind, glandular sac.” Loligopsis ocellata, Owen, too, shows a blind sac with a single duct for ingress and egress. Indeed this character seems common, so far as I have been able to discover; but the species at present under notice differs widely in having the “prostate” a thickened tube or canal with ingress at one end and egress near the other.

The duct of the “prostate” (fig. 1 c) is slender, and has transparent walls. It leads to the receptacle of spermatophores, into which it opens near its upper end.

The receptacle of spermatophores (b) is a large sac with thin transparent walls, and is usually packed with spermatophores and loose spermatozoa. It opens by a wide mouth into the penis (a) of whose base it appears to be a simple dilatation.

The penis tapers gradually towards its opening, which has an uneven, almost fringed margin.

When in sitû the vesicula seminalis and the duct of the “prostate” lie parallel to each other along the receptacle of spermatophores, to whose walls and to each other they are held by a membranous connection. The whorls of the prostate are held together by similar connections, so closely as to require the exercise of the utmost care to sever them without injury to the organ. The vesicula, duct, and receptacle of spermatophores thus held together lie transversely to the axis of the testis.

Spermatophores (pl. vi., figs. 3–7).—A common length of the spermatophores is about 9 lines, but this is often exceeded. The shape varies somewhat, but the general outline is the same. One end is thickened, often club-shaped, or with a knob; from this end the spermatophore tapers, but as the opposite end is approached there is often a slight dilatation and the end is obtuse, never, so far as I have been able to observe, filamentous. The outer case is transparent and of tolerable consistency. The thick end is mainly occupied by a sac containing spermatozoa, which extends for varying distances, but seldom, if ever, half the length of the spermatophore. To this sac is attached a sponge-like body of definite though slightly varying shape, resembling the turned handle of an awl. This body fits into the spermatophoric tube like a piston. From it extends towards the thin end of the tube a flat spirally coiled thread enclosed in a transparent case. The thread may extend to the thin end of the spermatophore and be there attached, or it may extend nearly to the end and then be recurved, or it may not extend right to the end.

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Professor Huxley (Anat. of Invertebrated Animals), on the authority of M. Milne-Edwards, describes the spring and the piston-like body as resembling the sponge of a gun with a spiral screw turned on the handle. I have carefully endeavoured to confirm this observation so far as the species under notice is concerned, but have not been able to do so. There seems to be always a spirally coiled thread encased in a transparent tube or sheath. The nearest approach to an axis bearing a screw is when the coils are thrown close together, as often happens. I have added a sketch (fig. 7) of a close portion of a coil, drawn from the ¼ in. objective with the camera lucida.

Female.—The only female specimen I have been able to obtain is a very small one (about 2 inch. in length) and much mutilated. The organs I have been able to observe are the long, narrow, nidamental glands, lying on the median line just above the gills, the oval flat and apparently stalked accessory glands immediately below them, and the ovary. The ovary in this specimen is very small and is somewhat pyramidal in shape, the apex lying at the upper end of the body. I am not sure that I have correctly observed the oviduct, but what I take to be the oviduct opens on the left side, having passed under the branchial heart.

(Note.—The fact that this specimen is the only female among ten that I have examined, and that the males were all fully ready for congress, would seem to show that sexual selection may have considerable scope among the members of this species.)

Alimentary System, (pl. vii.)

Mandibles (fig. 2).—Within the annular inner lip already noticed, are two vertical conchiolin jaws forming the beak, the posterior jaw overlapping the anterior one. The exposed parts are reddish-brown in colour, while the covered parts are transparent and colourless. Each jaw consists of an uncus, alæ and apophysis, the alæ being backward and lateral expansions of the uncus.

In the anterior or upper-jaw the uncus runs forward in a decurved line, terminating in a sharp point. The outer border of the alæ forms a continuous curve with this line, and runs backward to about half the length of the apophysis, from which it stands out prominently. The lower border of the alæ is a concave curve; and the front border, from the margin of the uncus, presents a waved outline. The apophysis extends downwards, its greatest length being at its outer margin. It is fully twice the size of uncus and alæ. Its inner border forms a convex curve, which extends round to the under-border, where it becomes concave.

In the posterior or under-jaw the uncus is not so large as that of the upper-jaw, is more obtuse, and is proportionately stouter. The alæ extend

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but a short distance backwards on the outer aspect, being here shortened by a concave border. At the sides they expand and become irregularly oblong in shape. They have a somewhat irregularly waved outline and extend forward beyond the uncus, so as to cover the inner portion of the alæ of the upper-jaw. The apophysis extends outwards and backwards with a slight curve, its shortest length being at the median line, where the margin is concave. Its greatest length is within, where the margin is convex. The apophysis slopes rapidly from the median line, leaving a well marked keel.

(Note.—In describing the jaws I have not adhered to the rule of speaking of the animal as though it were in a walking position, but have noticed them as they are detached and shown in the drawing.)

Taste-organ (fig. 3 a).—Within the jaws and on the posterior side of the mouth is the gustatory organ, showing a fairly well-marked division into two lobes. It is soft and uncurved, and under the microscope shows interlacing fibres.

Odontophore (fig. 3 b).—Next follows the broad radular band which works in and out of a socket in the centre of a raised papilla. It is armed with seven rows of silicious teeth. Its upper part is expanded, and has the margins recurved. The lower part has the margins incurved so as to form a cylinder, and it is probable that this part is but little used in mastication. The teeth on the upper part are stronger and stouter.

The central row of teeth consists of slightly curved, rather stout and obtuse spines, whose bases develope short obtuse prominences, one on each side, giving the denticles of this row a 3-fid appearance. The first lateral row consists of slightly curved spines, somewhat more acute than those of the median row. The spines have the base also developed as in the median row, but the inner basal spine is somewhat shorter than the outer. The next two rows consist of longer curved spines without basal spinules.

Faucial follicles (fig. 3 d). Next come the two “faucial follicles.” They are attached along one side, starting at the tongue and continuing to the commencement of the œsophagus. They are very well developed. The free margin is straight, and when folded over they form a covered channel over the radular socket.

Salivary glands.—The mandibles, tongue, odontophore, and faucial follicles are contained in the buccal mass, which narrows into the œsophagus. Outside the buccal mass, at the commencement of the œsophagus, are two slightly-raised papillæ, the lingual salivary glands. Further along the œsophagus, and imbedded in the liver, are two salivary glands with well-marked ducts.

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OEsophagus (fig. 1 c).—The buccal mass narrows into the œsophagus, which passes through the nerve-collar and peri-œsophageal cartilaginous ring, and is continued to the stomach without ingluvial dilatation. It dilates slightly as it enters the stomach.

Stomach (fig. 1 m).—The stomach is saccular and thick-walled. It shows two slight constrictions. The walls present on their inner surface strong longitudinal plicæ, which are prolonged into the intestine, and continue throughout its length.

Lying within the stomach is a loose tunic or sac with thick, though almost transparent, walls, showing longitudinal plicæ or corrugations. It has a wide orifice at one end, and at the other is thin or open. I have not been able to discover that it has any organic connection with the walls of the stomach, but as I have found it in all the specimens I have examined, I do not think its occurrence can be accidental.

The pyloric opening is at the lower end of the stomach and close to the cardiac opening. The commencement of the intestine is shown by a well-marked constriction. Neither cardiac nor pyloric opening is protected by a valve.

Pyloric cœcum (fig. 1 n).—Immediately following the constriction there is given off a long cœcal dilatation with thin but tough transparent walls. It expands at its attached end and tapers gradually to its opposite rounded extremity. When in sitû it forms a half curve round the stomach. As will be presently noticed, the hepatic ducts open into this cœcum. On the broadest part of its wall, at the attached end is a circular coat formed by a radiating mass, whose nature I have not discovered.

Intestine (fig. 1 h).—From the pyloric cœcum the intestine narrows gradually until the anus is reached. At somewhat less than half the distance between the cœcum and the anus it is folded over so as to form a distinct flexure. The anus has two stalked and leaf-like lateral valves.

Ink-sac (fig. 1 h).—The ink-sac is large and broad. Its highest and broadest part lies near the intestinal flexure, and from this part it narrows to its opening into the anus. Its coat is silvery and, in places, iridescent; and the dark sepia shows through the sac-walls. Throughout its length it is held closely to the intestine by a membrane.

Liver (fig. 1 f).—The liver is large, extending from immediately above the cephalic cartilage for about two-thirds of the length of the œsophagus. It is encased in a capsule showing under the miscroscope close fibres and yellow concretions. The liver itself is loose, and under the microscope shows clustered follicles and interlacing tubes with abundant yellow concretions. The bilobed condition is not observable.

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The hepatic ducts are two, and open close together into the commencement of the pyloric cœcum. They have developed upon them the light-coloured spongy “pancreatic” glands, which show under the microscope a loose fibrous tissue interspersed with yellow concretions (fig. 4). The fibrillar tissue is more loose and the yellow concretions larger, but less numerous, than in the liver. There is everywhere a network of ramifying tubes.

The whole of the organs are enclosed in a peritoneal membrane, which sends three mesenteric reflexions to the mantle, one of the arterial branches from the posterior aorta running along the anterior border of each reflexion.

Nervous System.

The main masses of the nervous system are aggregated into a large circular band (pl. vii., fig. 1 d) surrounding the gullet and lying in the aperture of the cephalic cartilage. On the anterior side of the gullet lie the cerebral and superior buccal ganglia, almost confluent and on the posterior surface are the inferior buccal, pedal, and parieto-splanchnic ganglia. The cerebral ganglion sends off optic nerves which enlarge greatly, forming the optic ganglia (pl. vii., fig. 1 e). I have not been able to discover the auditory nerves. From the parieto-splanchnic ganglia two nerves run, one on each side, towards the anterior aspect of the animal, passing under the columellar muscle and each forming on the back of the pallial chamber and at the side of the gladius a large stellate ganglion (fig. 1 g), which sends branches over the mantle. For about half their course the nerves to these ganglia are imbedded in the liver.

On the intestine, at the point where the pyloric cœcum is given off is a well-marked ganglion (fig. 1 l), which appears to be connected with the main nervous centres by a nerve following the course of the intestine. This ganglion gives off radiating fibres on all sides.

Eyes.

The eyes are lateral, are large and prominent and are covered by a transparent layer of integument. The eyeball is invested by a silvery tapetum composed of loose cells in two layers, one or both of which contain numerous refracting corpuscles. In front this passes into the loose iris, but I have not been able to observe any cartilage of the iris. The tapetum is lightly attached and can be easily removed. Then comes a thin, transparent, apparently muscular membrane, covering a thin cartilaginous coat which becomes thickened slightly in front. The membrane is not continued beyond the thickened front edge of the cartilaginous coat. Within the opening is suspended a cartilaginous ring, to which is attached a fringed radiating membrane having the lens in its centre. This is the corpus

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ciliare. The lens is surrounded by a deep groove, so as to form practically two lenses, the outer one being the smaller, the inner the larger and more convex. It is in the groove of the lens that the fringe of the corpus ciliare is attached. Within the eye is the fluid vitreous humour. The eye is lined by a delicate layer of loose cells, underlaid by a pigment layer, and then the inner layer of the retina.

Behind the eyeball, and forming as it were a cushion at its base, is a peculiar development of nervous tissue, the “white body.” It consists of rounded or irregular, apparently nucleated cells.

Auditory Organs.

In the substance of the cephalic cartilage are excavated two auditory chambers, one on either side of the ridge already referred to. Their walls give rise to several rounded protuberances, which are most numerous on the side nearest to the nervous ring. The two chambers approach each other on the posterior side, where the dividing wall becomes thin and transparent. Each contains a single large otolith, composed of carbonate of lime. The otoliths, (pl. viii., figs. 12–14) are somewhat flattened, and are similar in shape, though one is a little larger than the other. The main portion of the otolith has one of its margins markedly convex, while the other is roughened and uneven, with two fairly well-marked excavations. From this mass the otolith narrows to an end. All the surface, except the roughened part referred to, is white and smooth so far as can be seen with a pocket magnifier; but the microscope shows a rugose surface.

Explanation of Plates III.-VIII.

Plate III.—Sepioteuthis bilineata.

  • a, buccal membrane.

  • b, “oreille externelle.”

Plate IV.—Dissection along posterior surface, showing position of organs.

  • a, funnel.

  • b,b, hinge cartilages.

  • c,c, articular cartilages.

  • d,d, musculi retractores infundibuli.

  • e, penis.

  • f, intestine.

  • f′, ink-sac.

  • g,g, branchiæ.

  • h. descending aorta.

  • v,v, veins from the mantle.

  • k,k, branchial hearts with appendages.

  • l, ascending aorta with arterial branches.

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Plate III.—continued.

  • m, prostate gland.

  • n, vesicula seminalis.

  • o, receptacle of spermatophores.

  • p, testis.

  • q, stomach.

  • r, pyloric cœcum.

  • s, end of the gladius, exposed by tearing the membranous covering.

Plate V.—Circulatory and Respiratory Organs.

  • Fig.1.a, suspensory membrane of branchia.

  • b, vena cava.

  • c, descending aorta.

  • d, intestine, cut and turned aside to show branching of vena cava.

  • e,e’, left and right branches of vena cava, covered by renal organs.

  • f, branchial heart.

  • f’, appendage of branchial heart.

  • g, left lobe of renal organ. The opening is below; the tip of the blow-tube is inserted in the opening of the right lobe.

  • h, ascending aorta, with arterial branches.

  • k, cut edge of membrane encasing branchial heart.

  • Fig.2. Portion of a single branchial lamella, drawn with the camera Iucida from the 1 in. objective.

  • Fig.3. Portion of the last, drawn with the camera lucida from the ¼ in. objective, and showing the way in which the transverse capillary membranes of the lamellæ are folded.

Plate VI.—Male Organs.

  • Fig.1. Sketch of the male organs after the membranes holding the vesicula seminalis, duct of the prostate, and whorls of the prostate, have been severed.

  • a, penis.

  • b, receptacle of spermatophores.

  • c, duct of the prostate.

  • d, prostate gland.

  • e, vesicula seminalis.

  • f, vas deferens.

  • g, testis.

  • Fig.2. The prostate gland as in sitû;. The small figures, 1, 2, 3, 4, show the parts so numbered in fig. 1.

  • Fig.3. A spermatophore, natural size.

  • Fig.4. The same enlarged.

  • Fig.5. A portion of the same, drawn with the camera lucida from the 1 in. objective.

  • Fig.6. Another portion.

  • Fig.7. A close portion of a spiral coil from near the thin end of a spermatophore, showing a solid appearance. From the ¼ in. objective with the camera lucida.

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Plate VII.—Alimentary and Nervous Systems.

  • Fig.1. Sketch of Alimentary and main portions of Nervous System.

  • a, inner lip.

  • b, buccal mass.

  • c, œsophagus.

  • d, nerve collar.

  • e, optic ganglion.

  • f, liver.

  • g, ganglion stellatum.

  • h, intestine, ending in anus with lateral anal valves.

  • i, ink-sac.

  • k, pancreatic glands, along the course of the hepatic duct.

  • l, splanchnic ganglion.

  • m, stomach.

  • n, cœcum.

  • Fig.2. Mandibles.

  • a, anterior or upper.

  • b, posterior or lower.

  • Fig.3. Buccal mass cut open and mandibles removed. The point of the curved needle is inserted in the œsophagus.

  • a, taste organ.

  • b, odontophore, turned aside.

  • c, socket of odontophore.

  • d,d, faucial follicles.

  • Fig.4. Portion of pancreatic gland, drawn from the 1 in. objective with the camera lucida.

Plate VIII.

  • Fig.1. Gladius.

  • 2. Cephalic cartilage.

  • 3, 4. Neck cartilage, posterior and anterior aspects; showing attached muscular bands.

  • 5–9. Sections through 1st, 2nd, 3rd, and 4th right arms and clavate portion of tentacle. The dark line shows the extent of the chromatophoric surface.

  • 10. A single sucker.

  • 11. Section of the same.

  • 12. An otolith, natural size, on dark ground.

  • 13, 14. View of both surfaces of an otolith, much enlarged.

  • 15. The funnel cut open.

  • i, the infundibular valve.

Picture icon

Sepioteuthis Bilineata. H.B.Kirk.del.

Picture icon

Sepioteuthis Bilineata. H.B.Kirk.del.