462 CEPHALOPODA. 



them attentively, they are found to be composed of a number of 

 flattened circular discs appended to a lateral stem. Yet even all 

 these organs of touch form but a small part of the tactile apparatus 

 of the Nautilus Pompilius ; for the mouth, lodged within the oral 

 sheath, is surrounded with a series of tentacula even more nume- 

 rous than those appended to the exterior of the head. Around the 

 circular lip (Jig- SIS, m) which encloses the beak (w, o), are situ- 

 ated four labial processes (g 9 g, i, i) : each of these processes is 

 pierced by twelve canals, the orifices of which are disposed in a 

 single but rather irregular series along their anterior margin ; and 

 every one of these canals contains a tentacle similar to, but rather 

 smaller than, those of the external digitations (h, A, A-, A;), although 

 their structure is precisely similar. These cirri, like the former, 

 receive large nerves ; those supplying the external labial tentacles 

 being derived immediately from the brain (Jig. SIS, 6, 6), while 

 those distributed to the internal labial tentacles proceed from a 

 large ganglion (8) that is in communication with the cesophageal 

 ring through the intervention of a considerable nervous trunk (7). 



(502.) In the Dibranchiate Cephalopods none of the above- 

 described cirriferous processes are found to exist ; but there is every 

 evidence that the prehensile arms, and most probably the indivi- 

 dual suckers appended to them, are highly sensitive to tactile im- 

 pressions. Every one of the arms receives a large nerve, derived 

 from the same portion of the oesophageal collar as that which gives 

 origin to the tentacular nerves of Nautilus, which traverses its whole 

 length, lodged in the same canal as the great artery of the limb 

 (Jig- SOS). During this course the nerve becomes slightly dilated 

 at short distances, and gives off from each enlargement numerous 

 small nervous twigs which penetrate into the fleshy substance of the 

 foot. Immediately after entering the arm and producing the dila- 

 tations above alluded to, every nerve furnishes two large branches, 

 one from each side, which traverse the fleshy substance connecting 

 the bases of the arms, to unite with the nerves of the two conti- 

 guous arms, so that all the nerves of the feet are connected near 

 their origins by a nervous zone ;* an arrangement intended, no 

 doubt, to associate the movements of the organs to which these 

 nerves are appropriated. 



(503.) There is little doubt, from the character of the soft and 

 papillose membrane which forms a considerable portion of the sur- 

 face of the tongue, that in both the Nautilus and in the Dibran- 

 * Cuvier, M6moire sur le Poulpe, p. 36. 



