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Volume 23, 1890
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Art. VIII.—On the Anatomy of the Red Cod (Lotella bacchus).

Communicated by Professor Parker.

[Read before the Otago Institute, 9th September, 1890.]

Plates XII.-XV.

In this paper I propose dealing with the most important features in the general anatomy of our New Zealand Red Cod (Lotella bacchus). The original paper, which was written last year as a thesis for the honours examination of the New Zealand University, contains a quantity of matter which it has been deemed advisable to omit. This matter was simply a restatement and verification of the facts, in the anatomy of other Teleosteans, so well stated in our usual text-books, and therefore superfluous in a paper such as the present.

Lotella bacchus.

External Characters.—Form of lateral-line scales. Variation in fin formula.

Skeleton.—Articulation of dermal-fin rays with interspinous bones. Symmetrical tail. Cartilaginous parts of cranium.

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Enteric Canal.—Liver, spleen, gall-bladder. Relative position of chief organs. Peritoneum. Frozen sections.

Gills.—Pseudobranch.

Air-bladder.—Ridge from fontanelle to tip of cornu. Conveying sound-waves.

Urino-genital Organs.—Histology of lymphatic glands.

Circulatory Organs.—Third and fourth efferent branchial arteries unite.

Brain.

Auditory Organ.—Position of otolith, &c.

Parasites.—Tænia sp.(?). Nematoda (Filaria sp.?). Chondro-canthus lotella. Lernea lotella.

External Characters.—The lateral-line scales, besides differing from those covering the other parts of the body, also differ among themselves. They are generally of an oval form. Some, however, have an indentation at their posterior border. Others have a prolongation from their posterior ends, and are thus somewhat racket-shaped in appearance.

In regard to the number of dermal-fin rays and branchio-stegal rays there is considerable variation. I append the statements given, without any qualification, by Professor Hutton and by Dr. Günther, and some of the results obtained by myself:—

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Hutton: D., 10/41; A., 41; V., 6; B., 7.

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Günther: D., 10/42; A., 40; V., 6; B., 7.

Beattie: D., 10–12/39–45; A., 43–50; V., 5; B., 7.

From this table it will be noticed that, while both Hutton and Günther make out 6 rays in the pelvic (ventral) fin, I have been able to make out only 5 in the twenty-five to thirty specimens which I examined. Again, in not a single specimen have I got less than 43 rays in the ventral (anal) fin, while the numbers of Hutton and Günther are 41 and 40 respectively. In fact, in only four specimens did I make out 43. In all the others the numbers ranged from 44 up as high as 50, 45 and 46 being the predominating numbers. The numbers in the dorsal fin also show considerable differences. In the anterior part 10 seems to be the usual number, but in two specimens I counted 11 and in seven specimens I made out 12. In the posterior part I make 43 and 44 the most usual numbers. In only one specimen, and that a very young and small one, did I find 41, the number given by Professor Hutton; two had 42, one 39, and two 45.

Skeleton.—This agrees in the main points with the typical Teleostean skeleton. There are, however, certain modificacations. The most noticeable and perhaps the most interesting of these is the mode of articulation of the dermal-fin rays with the interspinous bones (fig. 10). Each interspinous

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bone is intercalated between two adjoining dermal-fin rays, its hatchet-shaped dorsal portion seeming to abut against or articulate with, on the one hand, the posterior edge of the base of a fin-ray, and, on the other hand, with the anterior edge of the base of the fin-ray immediately behind. Closer examination of a freshly-prepared skeleton, however, shows that the interspinous bone articulates not with two adjoining dermal-fin rays, but with two adjoining nodules of cartilage (a.c., fig. 10). These nodules are perfectly distinct, and lie in the hollow of the saddle-shaped base of the dermal-fin rays. Each is pear-shaped, and is in length about one-twentieth of that of the dermal-fin ray, and in breadth about one-third of that of the base of the dermal-fin ray. This cartilage seems to me to correspond with that found in the Ribbon Fish (Regalecus argenteus) by Professor T. J. Parker, and to which he refers as follows: “…. an ovoidal cartilage on which is perched… a dermal-fin ray. I have not met with cartilages of this kind in any fish which has come under my notice, and can find no account of any such in the works at my disposal. I regard them as representing a second or distal series of radials or pterygiophores, the interspinous bones forming the proximal series.”

Following the last undoubted caudal vertebra is a fan-shaped bone—the hypural. This bone, together with four others (two dorsal and two ventral), give the symmetrical appearance to the Teleostean tail. These bones, at first sight, appear to be flattened neural and hæmal spines; but they are attached, three to the last undoubted caudal vertebra and one to the hypural, by ligament only.

A very obvious cartilaginous nodule against which the posterior ends of the præmaxilla and maxilla abut is found in Lotella, and is identical with that found in Gadus. Curiously enough, as Professor Parker has pointed out, no mention is made of this in the leading authorities.

There is at the posterior part of the cranium on each side of the basioccipital a rather large aperture partly closed by a very thin lamina of bone. This aperture is bounded dorsally by the exoccipital, laterally and internally by the basioccipital, laterally and externally by the opisthotic, and ventrally by the basioccipital and opisthotic. This aperture opens into the auditory capsule, and will be referred to in the description of the air-bladder and auditory organ as the auditory fontanelle.

The cartilaginous parts of the cranium are situated in the ethmoid and auditory regions.

In the ethmoid region there is a median cartilage lying below the mesethmoid and above the vomer throughout the full length of the latter bone. This cartilage sends off processes into vacuities in the mesethmoid. About its centre it

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sends up an hourglass-shaped process which lies immediately behind the thick part of the mesethmoid, and extends up to the anterior face of the frontals. It also sends off side-processes into the parethmoids, these processes projecting outside at the articular facet for the palatine. The remaining cartilaginous parts of the cranium are contained in the auditory capsules. These extend to the outside by prominent processes, which issue at the facet on the cranium for the articulation of the hyomandibular.

The Enteric Canal.—From the mouth-cavity the gullet leads to the stomach, which occupies a considerable portion of the abdominal cavity, extending from its front wall backwards and downwards to the region of the anus. From the dorsal part of the stomach goes off the intestine, which is continued backwards for some distance. It then bends on itself and passes forward to the region of the stomach, thus forming the looped duodenum. It again bends on itself and passes backwards, forming the ileum and rectum, and finally ends at the anus (Pl. XII., fig. 1).

About ½in. posterior to the junction of the stomach and intestine are given off from the intestine, in the form of a circle, a few blind tubes. These are the pyloric cœca (py. c., figs. 1 and 10). From the examination of a number of specimens I conclude that the normal number of these pyloric cœca is six. However, that number is not constant. In one specimen the dorsalmost of these cœca at about 1in. from its blind end gave off a branch which ran almost parallel with, but not quite to the bottom of, the parent cœcum. Length of cœca, 2 ½in. Length of branch, ⅝in. In another specimen I found seven distinct cœca; while in still another I found eight, two of which were, however, much smaller than the others.

The mucous membrane lining the inside of the gullet varies from a whitish to a pinkish tint, and is thrown into a large number of longitudinal folds: that of the stomach is of a light-yellow colour, and is folded in all directions except a small area, just in front of the entrance to the intestine, which is absolutely devoid of folds.

At the entrance of the intestine there is a small flap which represents the pyloric valve (fig. 1).

Immediately posterior to this valve are the openings of the pyloric cœca. Each opens into the intestine by a separate aperture. From the posterior end of the ileum there passes into the rectum a very prominent valvular flap, the ileo-rectal valve (fig. 1).

The interior of each pyloric cœcum is lined by glandular mucous membrane of a rather brownish colour. The inside walls of the intestine are also lined with this glandular mucous membrane.

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The Liver: In the natural position of parts the liver covers almost the whole of the alimentary organs. It is attached at the anterior end of the abdomen, and terminates freely at the posterior end. It is a large yellowish-brown-coloured organ (fig. 3), consisting of a long left lobe (l.l.), a right lobe (r.l.) much shorter than the left, and a short middle lobe (m.l.). While agreeing with Gadus morrhua in these points, it differs in the fact that all three lobes are distinctly divided into lobules. Consequently the edges of the lobes have an irregular outline.

In the left lobe there are two rather large lobules, the anterior one (lob. 2) overlapping the posterior one (lob. 1). Each of these is again divided into a number of less marked and much smaller lobules.

The central lobe is divided into four very distinct lobules (lob. 1–4), while the right has two well-marked ones (lob. 1 and 2).

The spleen is a smooth dark-red body of elongated form lying dorsad of the stomach. The gall-bladder (fig. 2) is an ovoidal sac filled with bright-green bile, situated about the middle of the abdominal cavity towards the right side. From it there passes forwards the cystic duct, which almost at its anterior end dilates, forming a sac-shaped body (d.c.). At this point it is joined by the hepatic ducts from the liver.

There are nine of these hepatic ducts. The 8th and 7th and the 6th and 5th unite, forming each a common branch before opening into the cystic duct. The duct formed by the union of the cystic and hepatic ducts—the common bile-duct—opens into the intestine just beyond the pylorus.

The walls of the cystic duct are unequally thickened. I draw this conclusion from the fact that when the bile is forced through the duct the walls become covered with well-marked dilatations, giving them a regular tuberculated appearance.

The Relative Position of the Chief Organs: Through the kindness of Professor Parker I was permitted to avail myself of his privilege and have some specimens frozen at the Burn-side Refrigerating Works. They were kept in the chamber three days; the freezing operations at Burnside having been stopped the day I took my specimens. However, at the end of that time they were found to be sufficiently hardened. Sections were made with a small saw, each section wrapped in calico, and transferred to weak spirits for a few days before being mounted. From these sections, and by means of dissection, I have made out the topography of the chief organs as follows: The gullet passes from the mouth-cavity back into the stomach, which lies immediately below the air-bladder, and immediately above the ventral body-wall (fig. 10).

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The stomach extends nearly to the posterior end of the abdominal cavity. At about its middle it is separated from the air-bladder by a rather thin spleen. This, though dorsad of the stomach, lies somewhat to the right side (fig. 13). From the stomach passes off the coiled intestine, opening into which are the pyloric cœca. These cœca and the separate coils of the intestine are numbered and named in the drawings of the sections (figs. 10 to 15) in correspondence with the numbers and names in the figure of the enteric canal (fig. 1). The cardiac division of the stomach gives off (fig. 12) towards its ventral right side the pyloric division. This branch passes dorsalwards and then to the posterior end; coils on itself and forms the duodenum. This, again, turns and passes backwards, ending in the anus (fig. 14). From fig. 10 we see that the duodenum passes to the posterior end of the abdominal cavity. Both coils of the intestine lie on the right side, and the pyloric cœca lie on the right and ventral walls of the stomach. The disposition of the pyloric cœca is shown in figs. 12 and 13: 1 and 2 lie on the right side of the stomach; the remaining four lie ventrad of the stomach: 3, 4, and 5 are shown in fig. 12 opening into the pyloric division of the stomach.

The gall-bladder and the spleen are both dorsal to the coils of the intestine. The gall-bladder is posterior, and the spleen anterior. The cystic duct passes over the right side of the spleen, joins the hepatic ducts in the anterior region of the cavity, and then passes into the intestine immediately in front of the junction of the pyloric cœca.

The right lobe of the liver extends backwards about 1in. posterior to the hindermost end of the stomach, lies on the right side of it, and in the natural position of parts covers the gall-bladder, spleen, and part of the folds of the intestine. The left lobe is opposite to this, and extends to the posterior end of the abdominal cavity. In its natural position it covers the whole of the alimentary organs. The middle lobe lies immediately ventral to the stomach.

The liver, with its three lobes, completely surrounds the gullet. The middle lobe however is short, and in the region of the stomach the viscera are bounded laterally but not ventrally by the liver.

The organs of reproduction lie in the posterior part of the abdominal cavity, rather towards the left side (figs. 10 and 14). They lie below the air-bladder, and pass forwards to the dorsal region of the stomach.

The heart, in its pericardial cavity, is at the ventral anterior part of the body, and separated from the abdominal cavity by a vertical partition.

The sinus venosus occupies the posterior and ventral region

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of the organ. The auricle occupies the dorsal part, and the ventricle the ventral part.

The air-bladder extends throughout the whole length of the abdominal cavity, and lies below the vertebral column, from which it is separated throughout the greater part of its length by the middle kidney. At its posterior end it lies just below the rather thicker posterior kidney, and at its anterior end it is bounded above by the lymphatic glands. At its anterior end the air-bladder gives off two cornua, which, passing outwards and slightly upwards, end in a blunt extremity just posterior to the opercular bone.

Peritoneum: This consists of the usual parietal layer lining the body-cavity, and visceral layer reflected over the viscera. In the anterior two-thirds of the abdominal cavity, the peritoneum, which there lies on the outer side of the liver, is extremely delicate, and is closely attached to the liver, while in the posterior third, especially on the right side (the right lobe of the liver not extending to the posterior end of the abdominal cavity), it is quite free, and consequently can be easily made out. On the ventral face of the air-bladder in the middle line the two layers pass into one another, and from this point pass ventrally the various mesenteric attachments of the viscera, which are in strict agreement with those given for Gadus morrhua in Professor Parker's “Zootomy.” There are various invaginations of the visceral layer, which form peritoneal pouches for the various organs. One on each side passes between the liver and the stomach and intestine. On the right side the stomach and some of the folds of the intestine and gall-bladder are separated by a second pouch, and each gonad is enclosed in a separate pouch.

The Air-bladder.—The air-bladder covers the whole of the dorsal wall of the abdomen, the peritoneal lining of which is reflected over its ventral surface. The dorsal wall of this bladder is, especially in the middle and anterior regions, much thinner than the lateral and ventral walls.

The air-bladder passes from the posterior part of the abdominal cavity forwards right to the anterior part as a regular oval body. It then diverges dorsad, and to the right and left forming a right and a left cornu.

These cornua pass outwards and forwards until they reach almost the exterior (being separated from the outside merely by a thin layer of skin), just below the operculum in front of the dorsal end of the shoulder-girdle. They end blindly, and their anterior walls lie close against the posterior part of the cranium. The anterior face of the bladder, or, more strictly, of its cornua, towards the middle line is much thickened. This is especially the case at two points where a thick button-like body is seen. These button-like bodies are found to fit against

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the skull at the apertures of the auditory capsules (fontanelles) already referred to, to come into close contact with the lamina of each fontanelle and thus to completely close them. To quote from Professor Parker's paper in the “Transactions of the New Zealand Institute, 1882:” “Each cornu fits closely against the three facets of the skull, and is strongly attached by fibrous tissue…. The arrangements described must form a fairly-efficient transmitting apparatus for the organ of hearing. Sonorous vibrations, meeting the thin sub-opercular skin, will be transmitted to the air in the air-bladder and thence to the auditory fontanelle, the vibration of which will act immediately on the perilymph. The subopercular skin will thus act as an imperfect tympanic membrane, the air-bladder as a tympanic cavity, and the auditory fontanelle as a fenestra ovalis.” On the removal of the dorsal wall of the air-bladder, in sitû, there is noticeable a sort of cave, bounded anteriorly by the button-like body already referred to. This cave thus lies immediately posterior to the auditory fontanelle, and is especially noticeable, because between the two caves (i.e., at the median anterior part of the bladder), the dorsal, the anterior, and the ventral walls of the bladder are united and thickened, forming a solid bar-like body. From that portion of this thickened bar which lies mesiad of the two fontanelles there passes backwards and outwards to the posterior and extreme ends of each cornu a ridge formed as a thickening of the dorsal wall of the cornu. The inner end of this ridge forms the right or left—as the case may be—boundary of the cave referred to.

By this arrangement there is an imperfect partition between the main body of the air-bladder and its cornua, and I would suggest that the air-bladder is thus rendered a more perfect tympanic cavity than it would otherwise be. At any rate, it seems pretty certain that the ridge will, at least, have the effect of conducting the sound-waves to the auditory fontanelle.

Given off from the ventro-lateral walls of the air-bladder are a number of diverticula, which serve as means of attachment.

The rete mirabile extends forwards from about the middle of the bladder. At its anterior end it passes outwards and forwards in its own cornu. In a young specimen each rete mirabile is a distinct band, and the anterior end—that contained in the cornu—is separate from the posterior. In older specimens the two bands have grown together in the middle line, and the break at the anterior end is almost obliterated.

Urino-genital Organs.—The kidneys lie on the dorsal surface of the abdomen above the air-bladder, one kidney lying on each side of the vertebral column. They consist of two

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irregular longitudinal bands—the right one being the narrower—which pass at the anterior end into two brownish-red bodies, which lie dorsal and also partly anterior to the anterior end of the air-bladder. These improperly-called head-kidneys, to which I will refer again, come in contact with the posterior end of the skull; and also lie to some extent on its dorsal surface under the muscles. These bodies are the remains of the original pronephros. The remaining part of the kidney is mesonephros. At the posterior end the longitudinal bands—the middle kidney—unite and form a median mass lying posterior to the air-bladder, and enclosed in the first hæmal arch. This posterior kidney bends forwards and passes forwards and downwards for about 1 ½in. or 2in. From this part of the kidney goes off the ureter. Narrow at its posterior end, it widens to form two pouch-like diverticula—the urinary bladder,—and again gradually narrows to its opening behind the anus. The great difference between the kidney of Lotella and that of Gadus as figured by Smith and Norwell, in their “Illustrations of Zoology,” is seen in one of the middle kidneys of Lotella being narrower than the other, and also in the presence of the great posterior kidney which extends into the abdominal cavity below the air-bladder. This part seems to be entirely absent in Gadus. A microscopic examination shows that the middle and posterior parts of the kidney have the usual structure; but that the so-called head-kidney is absolutely devoid of kidney structure. The whole is composed of an aggregated mass of rounded very small cells, which, unlike the corpuscles seen in the blood-vessels, do not fit closely into one another. The structure is that of a simple lymphatic gland. Balfour, in the “Quarterly Journal of Microscopic Science,” vol. xxii., 1882, has described the same structure in several other fishes, with the exception that he found kidney tissue mingled with his lymphatic tissue.

Ovaries: These are two conical bodies uniting with one another posteriorly, and lying one on each side in the posterior part of the abdominal cavity. The ovaries send off from their posterior ends a common duct, which runs parallel with the ureter, and is separated from it by a very thin wall. The oviduct opens to the outside between the anus and the urinary aperture. The cavity of the ovary is filled with plate-like bodies, which are prolongations of its walls, and from the epithelium of which the ova are formed.

Of the male organs I can say nothing, for in working up this paper I never came across a male. This was no doubt due to the fact of the great preponderance of female fishes over males—a fact vouched for by Dr. T. W. Fulton in Geddes and Thomson's “The Evolution of Sex.”

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Circulatory Organs.—Here we have the purely typical Teleostean type. The only peculiarity and difference between Lotella and Gadus that I have been able to make out is that in Lotella the 3rd and 4th efferent branchial arteries unite and form a common trunk before opening into the left epibranchial artery.

Organs of Respiration.—The gills are four in number, and conform to the Teleostean type.

There is, however, also a rudimentary gill. This pseudo-branchia is seen as a small red patch covered with membrane and lying just under the operculum. Thus it is a little anterior to the dorsal end of the first branchial arch. On removing the membrane we see a rather irregular red body, usually with marked indications of a filamentous structure (fig. 4). But in some specimens examined absolutely no trace of filaments could be made out. In all cases, however, the blood-vessels to the pseudobranchs could be made out.

Brain.—Again we have a structure almost identical with that of Gadus morrhua.

I have noticed in all the specimens I examined a very thin cord of nervous matter passing, on each side, along the brain-membranes, and slightly dorsal to the brain. This cord unites the tenth nerve with the cutaneous branch of the fifth.

The so-called prosencephala have no trace of a cavity, and it seems perfectly justifiable, as stated by Rabl-Rückarat, to consider them as merely elevations on the floor of the prosencephala, the roof of which is formed by pia, and which is consequently very easily torn away, and is so in usual dissections of the brain. The microscopic anatomy seems to me to put all doubt out of the question. The brains were hardened in sitú, the bone decalcified, and sections made. In these sections (figs. 16 and 20) the pallium or roof of the prosencephala was well shown.

Auditory Organ (figs. 5 to 9).—The auditory organ consists of an ovoidal vestibule (v.) and three semicircular canals—two vertical and one horizontal. The vertical canals are anterior and posterior. Each canal starts from the top of the ovoidal vestibule with a swollen part—the ampulla—and passes upwards to the dorsal region of the auditory capsule. They then pass backwards and forwards respectively, and finally meet. Their adjacent limbs are thus confluent. The common limb then passes directly downwards, and opens into a swelling at the top of the vestibule. The horizontal canal (h.s.c.) lies entirely on the outer side of the vestibule, and opens into it by two separate openings. The ampullæ of the canals are situated at their extreme ends, those of the anterior and horizontal canals being anterior, and that of the

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Lotella Bacchus.

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Lotella Bacchus.

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Lotella Bacchus.

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Lotella Bacchus.

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posterior canal being posterior. The ampullæ of the anterior and horizontal canals open into a common branch, probably of the ovoidal vestibule. In this small pouch is a very small calcareous otolith—asteriscus (as.). The ovoidal vestibule also contains a large calcareous otolith—sagitta (s.).

It will be noted from my description that this auditory organ of Lotella bacchus differs very markedly from that of Gadus morrhua as figured by Professor G. B. Howes in Parker's “Zootomy,” and as figured by Smith and Norwell in their “Illustrations of Zoology.” Whereas in Gadus morrhua the small otolith, asteriscus, is contained in a separate pouch at the posterior end, in Lotella bacchus it is placed in a pouch at the anterior end, and a pouch which is in direct communication with the ampullæ of the anterior and horizontal semicircular canals. The utricle is not sharply marked off from the saccule. There is no trace of the cochlea of Gadus.

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Relation of Auditory Organ and Air-bladder (fig. 6): At its posterior end the ovoidal vestibule is somewhat flattened. This flattened part, which is composed of an exceedingly thin membrane, fits exactly and very closely against a thin, bony, and perfectly transparent membrane, l, which almost closes the auditory fontanelle. This bony membrane consists of two parts: one has its origin on the left side of the fontanelle, and passes parallel with the transverse axis of the cranium towards the centre of the foramen; the other has its origin on the right side of the fontanelle, and passes in like manner almost to meet its fellow of the opposite side. Fitting very closely against this bony lamina is the very thick button- or pad-like process of the air-bladder, already referred to. This button-like body, b, actually forms a sort of plug for the foramen. This plug is, in an ordinary-sized fish, about 1/10in. in thickness. Behind, this plug comes to cavity of the cornu of the air-bladder.

Parasites.—Large numbers of crustacean parasites were found attached to the gills. Others were attached by their star-like extremity to the mucous membrane of the mouth, and to the muscles of the body.

These parasites have been described by Mr. G. M. Thomson in the “Transactions of the New Zealand Institute,” vol. 22, pp. 368 et seqq. The former have been named by Mr. Thomson Chondrocanthus lotellæ, and the latter Lernea lotella.

Two tapeworms between 8in. and 9in. long were found in the intestine of one specimen—species of Tæia.

Nematoda: These worms were very numerous, and varied from 1 ½in. to 4in. in length. They were found mainly in the muscles of the cranium. One, however, was found between the olfactory lobes, while another was in the brain-case proper.

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One of the specimens was a pregnant female, and contained an immense number of young. Both the adult and the embryos agree in general characters with the figures of Filaria medinensis of Bastian and Leuckart, and seem to be a species of Filaria.

Description of Plates XII.-XV.

Lotella bacchus.
Plate XII.

  • Fig. 1. Enteric canal, distended with alcohol.

  • Fig. 2. Gall-bladder, showing the hepatic ducts.

  • Fig. 3. The liver (x ½), showing lobes and main lobules.

  • Fig. 4. Pseudobranch after the removal of the mucous membrane of the mouth.

Plate XIII.

  • Fig. 5. Auditory organ. (x 2.)

  • Fig. 6. Auditory organ in sitû, showing its relation to the air-bladder.

  • Fig. 7. The large otolith.

  • Fig. 8. The small otolith, from above.

  • Fig. 9. The small otolith, from below.

Frozen Sections.

  • Fig. 11. Through the body, just posterior to the supra-occipital spine. A posterior view.

  • Fig. 12. Through the anterior part of the stomach. An anterior view.

  • Fig. 13. Posterior view of the same section. The drawing is reversed so as to make it correspond with fig. 12 in. position.

  • Fig. 14. Through the anus. An anterior view.

  • Fig. 15. Through the posterior end of duodenum. An anterior view.

Plate XIV.
Frozen Section.

  • Fig. 10. A longitudinal vertical section, extending from the anterior end of the body to a short distance behind the posterior end of the abdominal cavity. This section, besides showing the main viscera, the heart, the air-bladder, the brain and spinal cord, in their relations, shows also the articulation of the interspinous bones and dermal-fin rays. The stomach is relaxed, and consequently the mucous membrane is thrown into folds.

Plate XV.

  • Fig. 16. A longitudinal vertical section of the brain, taken about the middle line. This is intended mainly to show the continuity of the cavities of the brain, and especially the relation of the cavity of the prosencephalon. It is partly after Weidersheim's figure from Rabl Rückard (the pineal body taken entirely from this figure).

  • Fig. 17. A transverse section through the anterior portion of the optic lobes of the brain.

  • Fig. 18. A transverse section through the epencephalon and metencephalon near the postcrior end.

  • Fig. 19. A transverse section further forward than fig. 18.

  • Fig. 20. A transverse section through the anterior part of the brain, showing pallium, commissure, &c.

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Key to Plates XII.-XV.
  • a.b. Air-bladder.

  • a.c. Articular cartilage.

  • Aq.Sy. Aqueduct of Sylvius.

  • as. Asteriscus.

  • a.s.c. Anterior semicircular canal.

  • au. Auricle.

  • a.v. Aortic valve.

  • a.v.v. Auriculo - ventricular valves.

  • b. Button-like process of air-bladder.

  • b.a. Bulbus arteriosus.

  • bn. Brain.

  • c. Centrum of vertebra.

  • c.b. Common branch of anterior and posterior semicircular canals.

  • cbl. Cerebellum (epencephalon).

  • ce. Prosencephalon.

  • c.m. Commissure between corpora striata.

  • C.st. Corpus striatum.

  • d.c. Dilated part of cystic duct.

  • d.f.r. Dermal-fin rays.

  • e.p. Pineal body.

  • Ep. Ependyma that lines the walls of the ventricle.

  • epcœ. Epicœle.

  • epen. Epencephalon.

  • f.G. Fornix of Gottsche.

  • G.p. Pineal gland, with its cavity Gp’.

  • h.s.c. Horizontal semicircular canal.

  • h.sp. Hæmal spines.

  • i.d. Intestine—duodenum.

  • i.i. Intestine—ileum.

  • i.r. Intestine—rectum.

  • i.sp. Interspinous bones.

  • J. Infundibulum.

  • l. Bony lamina.

  • Li. Lobi inferiores.

  • l.l. Left lobe of liver.

  • ly. Lymphatic glands.

  • mes.cœ. Mesocœle.

  • mesen. Mesencephalon.

  • met.cœ. Metacœle.

  • meten. Metencephalon.

  • m.k. Middle kidney.

  • m.l. Middle lobe of liver.

  • m.o. Medulla oblongata (metencephalon).

  • n.sp. Neural spines.

  • o. Ovaries.

  • Pa. Pia mater.

  • p.k. Posterior kidney.

  • pmx. Premaxilla.

  • prosen. Prosencephalon.

  • p.s.c. Posterior semicircular canal.

  • py.c. Pyloric cœca.

  • py.v. Pyloric valve.

  • R. Rete mirabile.

  • r.l. Right lobe of liver.

  • S. Sagitta.

  • s.a.v. Sinu-auricular valve.

  • sn. Spleen.

  • sp.c. Spinal cord.

  • s.ph.b. Superior pharyngeal bones.

  • st. Stomach.

  • s.v. Sinus venosus.

  • t. Optic lobes (mesencephalon).

  • T. Olfactory tracts at base of corpora striata.

  • tg. Tongue.

  • Tco. Roof of optic lobe.

  • t.s. Torus semicircularis.

  • v. Ventricle.

  • v.ao. Ventral aorta.

  • V. Vestibule.

  • Val. Valvula cerebelli.

  • Vcm. Common ventricle of prosencephala.

  • v.op.l. Ventricle of optic lobes.

In figures of the brain the pia mater is represented as a single brown line.