734 ZOOLOGY SECT. 



opens into the mantle-cavity, as already stated, by an orifice 

 which is not drawn out into a tube. There is no communication 

 between the cavities of the different sacs, and thus no median 

 chamber as in Sepia. The cavities are found to contain phosphate 

 of lime. Into each projects, from the corresponding afferent 

 branchial vein, a compact rounded group of venous appendages 

 (ren. cipp.\ consisting of two symmetrical portions. Internal to 

 these, each afferent vein has connected with it a second group of 

 glandular appendages, which are cylindrical or club-like in form ; 

 they project, not into the nephridial sac, but into the viscero-peri- 

 cardial compartment of the ccelome. They have been compared 

 with the appendages of the branchial heart of Sepia, but differ in 

 their relations to the renal appendages. 



Nervous system. Nautilus differs strikingly from Sepia, and 

 resembles Chiton (p. 667) in the form assumed by the central 

 parts of the nervous system, distinct ganglia being absent. A very 

 thick nerve-collar, the posterior portion of which is double, surrounds 

 the oesophagus just behind the buccal mass. The anterior part of 

 the collar (Fig. 642, cer. g.) represents the cerebral ganglia, the 

 oral portion of the posterior part (pcd. g.) the pedal, the aboral 

 portion (pi. g.} the pleuro-visceral, while the lateral parts, not* 

 distinctly marked off from the rest, represent the cerebro-pedal and 

 cerebro-pleural connectives. From the cerebral "'ganglia" pass 

 nerves to the buccal mass, to the olfactory organs (plf. n.) the 

 otocysts, and a pair of very thick optic nerves (opt. n.) to the eyes. 

 The pedal ganglion gives off numerous nerves to the tentacles 

 and the funnel. The pleuro-visceral gives origin to pallial and 

 visceral nerves. 



Sense Organs. The otocysts are a pair of sacs embedded in 

 recesses close to the cerebral ganglia; each contains a number 

 of small fusiform otoliths. An olfactory function is ascribed to a 

 process having the appearance of a modified tentacle, situated on 

 the aboral side of the eye. Various parts connected with the foot 

 have also been supposed to be olfactory, but the marked sexual 

 differences which they present render this improbable. The 

 osphradia (p. 729) contain ganglion-cells and are undoubtedly 

 organs of special sense. 



The eyes, situated at the sides of the head, are very large, but 

 extremely simple in structure, presenting a marked contrast to 

 those of Sepia, and scarcely comparable to those of any other 

 animal, with the exception perhaps of Patella (p. 694). Each is 

 of the shape of a saucer attached to the head by its convex side 

 through a short thick stalk, the mouth being closed in by a 

 slightly convex disc, with a circular aperture about its centre. A 

 slight, raised rim runs round close to the margin on the posterior 

 half, and a narrow groove runs inwards from this to the central 

 aperture. In the interior of the cup is neither lens, vitreous 



