Art. XX.—Notes on the Anatomy of the Bitentaculate Slugs of New Zealand.
[Read before the Philosophical Institute of Canterbury, 3rd March, 1881.]
In the “Transactions of the New Zealand Institute,” vol. xi., p. 332, I described a new genus of bitentaculate slugs under the name of Konophora. This year, through the kindness of Professor Parker, I have been enabled to examine another specimen, and find that after having been in spirit for some time a lateral groove appears dividing the body from the foot, as in Janella, and that the anatomy is so like that of J. bitentaculata that a new genus seems hardly necessary for its reception. I therefore propose to regard Konophora marmorea as a species of Janella, distinguished from the other two species by not tapering rapidly to the tail, by its conical eyepeduncles, and by the form of the central row of teeth, as described further on.
The only specimen of J. papillata that I have had for dissection was in such a bad state of preservation that I was unable to make out the details of the alimentary and reproductive systems, but I saw enough to convince me that they are constructed essentially on the same plan as those organs in the other two species; in fact I think that it may be only a variety of J. bitentaculata. I propose, therefore, to give a general account of the anatomy of the genus, and also to point out the differences between J. bitentaculata and J. marmorea. I have to thank R. W. Fereday, Esq., for living specimens of J. bitentaculata which he found on flax (Phormium) at Fendal Town, near Christchurch.
External characters. The anus is situated on the right side, below and a little in front of the pulmonary opening. The reproductive organs open behind the right eye-peduncle, (fig. 1). There is a mucous pore situated on the dorsal groove, just in front of the pulmonary opening. The foot is scarcely distinct from the body, and shows no locomotive disc, but after the animal has been placed in strong spirit a lateral groove appears on each side, and the foot shows three longitudinal grooves, a broad central one, and a narrow one on each side, (fig. 2). Twelve to sixteen minute calcareous plates form a rudimentary shell. They are situated inside the pulmonary cavity; the largest in front of the opening, and the others forming a row on the inner or left side of the opening, (fig. 16). These particles have been figured by Dr. Knight, (“Trans. Lin. Soc.” xxii., p. 381.)
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Alimentary system (figs. 4 and 5). The buccal mass is large, and of the ordinary shape, but the retractor muscles arise from the musculature of the foot, immediately under the nerve collar. The length of the radula is not quite twice its breadth, and each half is rolled up into a separate spiral (fig. 4 c), as figured by Dr. Knight in his paper already quoted. The teeth are about 255–1–255, varying slightly in number, and there are about 130 transverse rows. The central tooth is about 1/1000 of an inch in length, and varies considerably. In J. marmorea the anterior end is emarginate, and there is no central cusp (fig. 9). In J. bitentaculata there is a central cusp, and the anterior end is either simple or has a central swelling, which is either single or divided into two (figs. 10, 11, and 12). In the single specimen I had of J. papillata the central teeth were like figs. 10 and 11, but none like fig. 12. There is no distinction between lateral and marginal teeth (figs. 13 and 14); all are alike, and similar in all the species. They have been very accurately figured by Dr. Knight. The inner laterals are rather more than 1/1000 of an inch in length, and they gradually diminish to about half that size at the margin. They are arranged on the radula in transverse lines that form an obtuse angle, pointing anteriorly. (fig. 8).
On each side of the œsophagus there is a large salivary gland (fig. 5 c), the ducts opening into the posterior portion of the buccal mass. Below the buccal mass and œsophagus lies a peculiar tongue-shaped organ (fig. 4 d), which is ductless, and fastened in its anterior half to the body wall, but free posteriorly. It is composed of rounded nucleated cells, and is grooved along its upper surface. It may represent the organ of Semper in other slugs.
The stomach is long, and makes nearly three right-hand spiral turns. It passes gradually into the intestine, which turns forward, and follows the stomach back through its windings to the œsophagus; it then turns suddenly back, round the posterior branch of the aorta (fig. 5 f), and again descends nearly to the end of the stomach; it then turns suddenly forward, and once more following the convolutions of the stomach, ends in a short straight rectum, which opens on the right side below and in front of the respiratory opening. The liver (fig. 5 e) is formed of two compact spindle-shaped lobes. In J. marmorea the intestine turns forward immediately after receiving the hepatic ducts, but in J. bitentaculata it descends nearly to the posterior end of the liver, making another half turn before it turns forward.
Reproductive system (fig. 7). The ovotestis is subrotund in form and divided longitudinally below by a groove running from the hermaphrodite duct, which is purplish. It is of a dead white or pale yellow colour. It is remarkable for its position in the animal, lying in front of the rectum, while in all other slugs with which I am acquainted it is placed posteriorly, among the folds of the liver. The albumen gland is long and tongue-shaped, and of a pale yellow. In J. marmorea there are two other large accessory glands at its base, but these are absent in J. bitentaculata. It is, however, quite possible that these so-called accessory glands may be folds of the oviduct which I was unable to unravel. The vas deferens separates from the oviduct at its commencement in J. marmorea, and at about the middle in J. bitentaculata. If the supposed accessory glands in J. marmorea are but folds of the oviduct, then the vas deferens would separate in the same position in both species. The penis is long, narrow, and tapering, and the vas deferens enters it at its posterior extremity. The retractor of the penis (fig. 7 k) arises from the musculature of the foot, on the left side, in a line with the respiratory opening; it is inserted into the posterior extremity of the penis. The spermatheca (fig. 7 g) is purplish brown, globular, with a short neck; it is situated on the oviduct, a short distance from the genital opening. The penis lies across the animal's neck, over the nerve collar. The spermatozoa are gradually thickened at one end, which is spirally twisted. In J. marmorea the ovo-testis lies on the upper surface, and is exposed when the animal is opened from the back; in J. bitentaculata it is hidden, but can be seen from below.
Excretory and circulatory systems (fig. 15). The pulmonary cavity is closed internally by a delicate membrane, slightly radiately plicated, and lies centrally in the animal. The heart is immediately to the left, and outside it. The ventricle is yellow, the auricle colourless. The aorta divides immediately into anterior and posterior branches. The renal organ is double, and lies behind the pulmonary chamber. The duct from the right organ passes over to the left, where it joins the duct of the left organ, and both open by a common duct into the respiratory cavity.
Nervous system (fig. 6). This is very compact and concentrated. The parieto-splanchnic and pedal ganglia are in contact, but not fused together. The whole nerve collar is white. The right peduncular nerve passes over the oviduct, close to the genital opening (fig. 7 h). The auditory vesicles are placed on the outer margins of the pedal ganglia.
Explanation of Plate V.
Janella marmorea, natural size. a. pulmonary orifice; b. anus; e. opening of reproductive organs; d. eye peduncles; e. mucous pore.
The same. Section across body after having been in spirit, showing the three-grooved foot.
The same laid open. a. buccal mass; b. penis; c. ovo-testis; d. vas deferens; e. hermaphrodite duct; f. albumen gland; g. rectum; h. stomach and intestine; i. liver; k. pulmonary opening.
The same; buccal mass from the side. a. buccal mass; b. œsophagus; c. odontophore; d. organ of Semper.
The same; alimentary system. a. buccal mass; b. commissure of cerebral ganglia; c. salivary glands; d. rectum; e. liver; f. posterior branch of aorta.
The same; nerve collar. a. commissure of cerebral ganglia; b. eye peduncle retracted; c. auditory vesicle.
The same; reproductive system. a. ovo-testis; b. hermaphrodite duct; c. albumen gland; d. oviduct; e. vas deferens; f. penis; g. spermatheca; h. peduncular nerve; i. opening of reproductive organs; k. retractor muscle of penis.
The same; radulalaid open, magnified five times. a. anterior end; the dotted lines show the direction of the transverse rows of teeth.
The same; central tooth, magnified 700 times.
|Figs. 10 and 11.||
Janella papillata; central teeth magnified 700 times.
Janella bitentaculata; central tooth magnified 700 times.
The same; lateral tooth, magnified 700 times.
Side view of the last.
The same; excretory system, from below. a. pulmonary chamber; b. heart; c. anterior branch of aorta; d. posterior branch of aorta; e. renal organ; f. anus.
The same: rudimentary shell, from below. a. respiratory orifice; b. calcareous plates forming the shell.