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Show 124 MR. W. E. HOYLE ON T H E [Mar. 5, reached a more advanced stage. Another observation, too, indicates beyond a doubt that the process of pen-formation has proceeded further in this specimen than in the other. At the base of this cone the epithelium has been retracted away from it, and on the surface thus liberated could be seen a film of highly refractive material (sep.). A similar film is also discernible on the ventral aspect of the base of this cone, and they both become thinner and disappear as they pass towards the centre of the base. I think it is safe to conclude that we have here the incipient formation of the phragmocone which is known to be present at the posterior extremity of the pen of Gonatus. The conical mass of degenerate cartilage then serves the purpose of a mould upon which the septa of the phragmocone are deposited. Near the middle of the granular mass was a curved band of apparently denser material than the rest, in the centre of which a faint line could be traced. Whether this is merely accidental or whether it indicates the position of an earlier incomplete septum I have no means of ascertaining. V. The Muscles. Regarding the disposition of the muscles not very much is to be said; on the whole it resembles the arrangement found in Onychoteuthis and Enoploteuthis, but differs from both these in certain respects. The capsule of the liver, formed by the retractor muscles of the head, is much less strongly developed than in Onychoteuthis, the lateral portions being, to all appearance, merely membranous without any muscular fibres. The retractores capitis mediani arise separately in their usual situation near the middle line ; as they pass forward they approach each other and fuse together a short distance behind the point at which the cephalic aorta enters them ; in front of this they are again easily separable. In a specimen of Onychoteuthis banksii which was examined for the sake of comparison there is a union in the same place, but less complete. The retractores capitis laterales are slightly developed and they seem to be distinctly separated from the median retractors by a membranous interval in the capsule of the liver. No muscle is present running from the head to the ventral surface of the pen-sac, and passing over the commissure between the two ganglia stellata, such as is described by Brock 1 in the case of Enoploteuthis. The collaris muscle has the usual disposition and relations. The adductor infundibuli inferior has pretty much the same arrangement as in Onychoteuthis. It arises far forwards and some distance from the ventral line, and is inserted nearly in the middle line a little distance behind the posterior infundibular nerve. VI. The Nervous System and Sense-Organs. The central nervous system (Plate XIII. figs. 1, 2) resembles most 1 Brock, " Versuch einer Phylogenie der dibranchiaten Cephalopoden " Morph. Jahrb. vi. p. 198 (1880). |
