SENSE OF SMELL. 589 



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 (V). 



(1578.) 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 individual suckers appended 

 to them, are highly sensitive to tactile impressions. Every one of the 

 arms receives a large nerve, derived from the same portion of the 

 O3sophageal 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. During this course the nerve becomes 

 slightly dilated at short distances, and gives off from each enlarge- 

 ment numerous small nervous twigs which penetrate into the fleshy 

 substance of the foot. Immediately after entering the arm and under- 

 going the dilatation 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 

 contiguous 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. 



(1579.) There is little doubt, from the character of the soft and 

 papillose membrane which forms a considerable portion of the surface 

 of the tongue, that both in the Nautilus and in the Dibranchiate Cepha- 

 lopods the sense of taste is sufficiently acute far superior, indeed, to 

 what is enjoyed by any of the Gasteropod Mollusca, and possibly even 

 excelling that conferred upon fishes and others of the lowest Vertebrata 

 that obtain their food under circumstances such as render mastication 

 impossible, and the perception of savours a superfluous boon. 



(1580.) That the CEPHALOPODA are provided with a delicate sense of 

 smell, and attracted by odorous substances, is a fact established by the 

 concurrent testimony of many authors, although in the most highly 

 organized genera nothing analogous to an olfactory apparatus has as yet 

 been pointed out : nevertheless, in Nautilus, Professor Owen discovered 

 a structure which he regards, with every show of probability, as being a 

 distinct organ of passive smell, exhibiting the same type of structure 

 that is met with in the nose of fishes, and, from the circumstance of its 

 being the first appearance of an organ specially appropriated to the per- 

 ception of odours, well deserving the attention of the physiologist. We 

 may here premise that the exercise of this function in creatures con- 

 tinually immersed in water must depend upon conditions widely differ- 

 ing from those which confer the power of smelling upon air-breathing 

 animals. In the latter, the odorant particles, wafted by the breeze to a 

 distance and drawn in by the breath, are made to pass, by the act of 

 * Cuvier, Memoire sur la Poulpe, p. 36. 



