HEARING. 309 



interior view of the same membrane (f,) with the vestibule 

 (v) laid open, and the auditory nerve (n) passing through 

 the shell to be distributed on the sacculus. 



It appears from a variety of observations that Insects, both 

 in their larva and their perfect state, possess the faculty of 

 hearing; but no certain knowledge has been obtained of tbe 

 parts which exercise this sense. Tlic prevailing opinion 

 among entomologists is that it resides in some part of the 

 antennae; organs, which are supposed to have a peculiar sen- 

 sibility to aerial undulations. This hypothesis is founded 

 principally 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 Mollusca appear to possess, even in the small- 

 est degree, the sense of hearing, if we except the highly or- 

 ganized Cephalopoda; for in them we find, at the lower part 

 of the cartilaginous ring, which has been supposed to exhi- 

 bit the first rudiment of a cranium, a tubercle, containing in 

 its interior two membranous vesicles, contiguous to each 

 other, and surrounded by a fluid. They evidently corre- 

 spond to the vestibular sacs, and contain each a small calca- 

 reous body, suspended from the vesicles by slender nervous 

 filaments, like the clapper of a bell, and probably performing 

 an office analogous to that instrument; for, being thrown 

 into a tremulous motion by every undulation of the sur- 

 rounding fluid, they will strike against the membrane, and 

 communicate similar and still stronger impulses to the 

 nerves by which they are suspended, thus increasing the 

 impression made on those nerves. The mechanical effect of 

 an apparatus of this kind is shown by the simple experiment, 



• Camparetti has described structures in a great number of insects, which 

 he imagined were organs of hearing; but liis observations have not been con- 

 firmed by subsequent inquirers, and their accuracy is therefore doubtful. 

 See De Blainville " De I'Organisation des Animaux," i. 565. 



