82 



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 tbese tentacles, must be 

 both sensory and motor ; they are 

 in connection with a large double 

 ganglionic mass (h h) situated 

 beneath the oesophagus but in 

 front of the other sub-oesophageal 

 ganglion (c c), which is thought 

 by Owen to represent "the liomo- 

 logues of both the branchial and 

 pedal ganglions in the inferior 

 Moll u sea." The latter pairs of 

 ganglia are clearly combined in 

 function, since the locomotions of 

 the Nautilus, like the much more 

 rapid locomotions of other Cepha- 

 ncipally eftected " in a succession 



Fio. 28. — Nervous System of 

 Pearly Nautilus. (Gegenbauer 

 after Owen.) a a, Cerebral gan- 

 glia, constituting the brain ; o o, 

 optic ganglia in communication 

 with cerebral ganglia, which are 

 also connected with a lower gang- 

 lionic mass(/j b), receiving nerves 

 (( (') from the tentacles and other 

 pirts about the muutli, partly 

 sensory and partly motor. The 

 cerebral ganglia are in addition 

 united to a posterior sub-ceso- 

 phageal mass (c c), supposed to 

 represent a pair of pedal and a 

 pair of branchial gan^jlia. m m. 

 Motor nervts; d d, branchial 

 nerves and ganglia. 



lopods, seem to be pri 



