43G THE SENSORIAL FUNCTIONS. 



state, possess the faculty of hearing ; but no 

 certain knowledge has been obtained of the 

 parts which exercise this sense. The prevailing 

 opinion among entomologists is that it resides in 

 some part of the antennae ; organs, which are 

 supposed to have a peculiar sensibility to aerial 

 undulations. This hypothesis is founded princi- 

 pally on the analogy of the Crustacea, whose 

 antennae contain the vestibular cavity already 

 described ; but on the other hand it is opposed 

 by the fact that Spiders, which hear very acutely, 

 have no antennae ; and it is also reported that 

 insects, when deprived of their antennae, still 

 retain the power of hearing.* 



None of the MoUusca appear to possess, even 

 in the smallest degree, the sense of hearing, if 

 we except the highly organized Cephalopoda ; 

 for in them we find, at the lower part of the car- 

 tilaginous ring, which has been supposed to ex- 

 hibit the first rudiment of a cranium, a tubercle, 

 containing in its interior two membranous vesi- 

 cles, contiguous to each other, and surrounded 

 by a fluid. They evidently correspond to the 

 vestibular sacs, and contain each a small cal- 

 careous body, suspended from the vesicles by 



* Comparetti has described structures in a great number of 

 insects, which he imagined were organs of hearing ; but his 

 observations have not been confirmed by subsequent inquifers, 

 and their accuracy is therefore doubtful. See De Blainville 

 " De rOrganisation des Animaux," i, 565. 



