NERVOUS SYSTEM. INVERTEBRATA. 59 



D. 60. The anterior or muscular part of the body of a female 

 Pearly Nautilus (Nautilus pompilius) laid open longitudin- 

 ally along the dorsal aspect, and with the sides divaricated 

 to show the nervous system. 



In the female the inner ring of tentacles consists not 

 only of two lateral groups, as in the male, but also of a 

 ventral series located in two lobes that lie one on either 

 side of the ventral mid-line. 



A pair of large nerves (the left one is indicated by black 

 paper) for the innervation of these are given off from the 

 anterior suboesophageal band on the outer side of the funnel- 

 nerves. Each enlarges as it nears the tentacular lobe to 

 form a triangular ganglion, from which branches radiate 

 to the individual tentacles. 0. C. 1306 A. 



Owen, Memoir on the Pearly Nautilus (Nautilus 

 pompilius), 1832, p. 36. 



D. 61. The head of a Cuttle-fish (Sepia officinalis) dissected from 

 the dorsal aspect to show the form and position of the 

 central nervous system. It is extremely concentrated, 

 and forms a compact ring around the fore part of the 

 oesophagus protected externally by a cartilaginous capsule. 

 The ring is divisible into a pyriform supra-oesophageal 

 mass (cerebral ganglion) and a larger oblong suboesophageal 

 ganglion, united together on either side of the oesophagus 

 by stout connectives. 



The cerebral ganglion is joined on either side by a short 

 stalk to a large kidney-shaped optic ganglion, from whose 

 distal margin a number of nerve-fibres arise and perforate 

 the cartilaginous optic capsule to reach the retina. Upon 

 the dorsal surface of each optic stalk there is a small 

 rounded excrescence from which the olfactory nerve takes 

 its origin (see Olfact. Organs, Section E). Upon the right 

 side bristles have been placed beneath the superior ophthalmic 

 nerve a small nerve that rises from the hinder part of the 

 suboesophageal mass close to the base of the circum- 

 oesophageal connective, and innervates the globe of the eye 

 and the integument on its dorsal surface. 0. C. 1306 D. 



