THE FACULTY OF HEARING. 361 



the nerve fibres are spread out in great numbers over a very 

 remarkable development of elastic tongues or processes of 

 membrane lining the ducts of the cochlea, which, like the ampullae 

 and sac, contain fluid. In the am;pullce are found cells and bristle- 

 like filaments fcirrhij developed from the lining epithelial mem- 

 brane in whose substance the embedded nerve-ends communicate 

 with the cells. Thus in the amimllcQ and cochlear organs the 

 " cirrhi " and membranous processes (pillars of Corti^ — so named 

 after their discoverer) thrown into motion by the passing wave of 

 fluid may agitate the nerve cells. In this vestibular sac are a few 

 minute *' otoliths" suspended in the fluid content, and the nerve- 

 ends with which these otoliths come in contact must be tapped by 

 them on the slightest wave movement of the fluid. 



The cochlear organ is found in mammalia, birds and reptiles. In 

 fishes the vestibular sac is large, and the nerve ends come in 

 contact with otoliths, which take the place of the bristle-like 

 filaments of the membrane lining the ampullae. The otolith 

 consists of a hard or pasty mass of minute prisms of calcic 

 carbonate in the form of Arragonite, and is suspended free in the 

 viscid endolymph which occupies the cavity of the sac. A true 

 cochlea is absent in fishes. The occurrence of otoliths is constant 

 throughout the whole series of vertelrata, and amongst invertebrata 

 crabs have been found to possess a skin pouch, inside of which are 

 otoliths, and outside of it a plexus of nerves. It is impossible to 

 doubt the inference of homologous structure and of an auditory 

 function when we compare this otolith sac with the ear of the fish, 

 or even the labyrinth of the mammal ear. 



Turning now to the tympanal structure of the orthopterous 

 insects, it will be sutiicient for our present purpose of noticing any 

 analogies and homologies which may be established with other 

 auditory organs, to describe its principal anatomical features, 

 leaving the description of minute detail and the full explanation 

 of the diagrams exhibited, to a later opportunity.* The organ in 



* In the present paper the desci-iptive anatomyof the tympanal organ is omitted 

 as it ■would be quite unintelligible without illustration by numerous figures. 



