THE NERVOUS SYSTEM OF MOLLUSKS. 



relations of auditory organs in this animal have not been 



Definitely settled. 



In regard to organs of taste and 

 touch, Owen writes as follows, 

 " The complex and well developed 

 tongue of the Pearly Nautilus ex- 

 hibits in the papillae of its anterior 

 lobes and in the soft ridges of its 

 root the requisite structure for the 

 exercise of some degree of taste : 

 . . . the sense of touch must be 

 specially exercised by the numer- 

 ous cephalic tentacles, which, from 

 their softness of texture, and 

 especially their laminated inner 

 surface, are to be regarded as 

 organs of exploration not less than 

 as organs of prehension." The 

 nerves of these tentacles, must be 

 both sensory and motor ; they are 

 in connection with a large double 



FIG. 28. Nervous System of /i r\ M. i. a 



Pearly Nautilus. (Gegenbauer gangllOniC maSS (6 6) Situated 



after Owen.) a a, Cerebral gan- b enea th the OeSOphagUS but in 



glia, constituting the brain ; o o, 



optic ganglia in communication fl'Ont 01 the other SUD-OeSOpnageal 



with cerebral ganglia, which are o-l \ w hi cn ig thought 



\ 



( cc \ 



also connected with a lower gang- (C C), 



lionic mass (6 6), receiving nerves by Owen to represent "the homo- 

 p^r^t^^out^p^y logues of both the branchial and 

 sensory and partly motor. The p e( j a i ganglions in the inferior 



cerebral ganglia are in addition * .. ,. mi , , - f 



united to a posterior sub-oeso- Mollusca. The latter pairs of 

 phageai mass (CC ) supposed to , { clearly combined in 



represent a pair of pedal and a c J 



pair of branchial ganglia, m m, function, since the locomotions of 



' * " ' the NautfluB, like the much more 

 rapid locomotions of other Cepha- 

 lopods, seem to be principally effected " in a succession 



