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Show 1889.] ANATOMY OF GONATUS FABRICII. 119 5. The Gladius is narrow and linear anteriorly, but broader and lanceolate in the hinder two thirds, whilst it ends posteriorly in a hollow cup or cone, which has several diaphragms within it, and is not covered outside and behind by a solid chitinous spine as is the case with most, perhaps all, Onyclioteuthids ; at all events no species hitherto known has such a hollow cone. 6. The Fins extend some distance beyond the hinder end of the body, and their firm saddle-shaped cartilage slides upon the terminal portion of the gladius. 7. The Radula has only five rows of teeth, instead of the usual seven. II. General Disposition of the Organs. The mantle-cavity is very extensive, reaching backwards almost to the end of the caudal extremity ; when it is opened the following arrangement of parts may be observed (Plate XIII. fig. 5). The siphon is of the usual form, having a valve, as has already been recorded by several observers, although Gray denied its existence. The two retractor muscles of the siphon (depressores infundibuli, m, m) are seen stretching backwards from its base on either side, and external to them are the gills (br.), which are very long and fixed to the mantle almost as far as their ends. Attached to the base of the siphon, to the lateral aspect of the head, and to the mantle in the middle line above is the usual valvular flap formed by the collaris muscle, which prevents the egress of the water from the lateral parts of the mantle-cavity. The ink-sac (i.s.) lies in the middle line and extends forwards almost to the anus (a.) : in the larger specimen it was quite fragmentary, but appeared to reach further backwards than in the small ones, in which, moreover, it was somewhat obliquely placed. The rectum passes over it forwards from right to left, and the anal flaps (in the small examples) are simple in form, and taper gradually from the base to the apex. The vena cava (v.c.) lies along the right side .of the digestive gland ("liver" of most authors). Through the renal sac may be seen the sacculations on the vena cava (re.) and the branchial hearts (br.h.) in their usual situation. The renal openings seem to be minute papillse, situated just in front of the branchial hearts, as in Onychoteuthis. One of m y specimens showed them, and I was able with some difficulty to make out their position in a specimen in the British Museum. The apertures of the oviduct (Plate XIII. fig. 3, od.) are deeper than and external to the branchial hearts, and the nidamental glands may be seen in the middle line immediately posterior to the renal organs: the posterior aorta passes out between their diverging hind extremities. In the smaller specimens the stomach (s) could be discerned in the middle line behind the bases of the gills ; the genital gland when fully developed appears to cover it. III. The Cartilages. The Cephalic Cartilage.-Two heads of larger specimens were 9* |
