1 84 PHYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



to that of birds, but the interior ear has lost, or nearly 

 lost, the cochlea. 



In amphibians the whole of the mid-ear as well as 

 the exterior ear is lost ; only the interior ear remains, 



A 



...ty 



Fig. 117. — A, tibia of a grasshopper (Meconemia), with auditory organ. 

 B, section oi the same enlarged : /y, tympanic membrane ; auv, audi- 

 tory vesicle ; gc, ganglionic cell. (From Packard. ) 



and this is reduced to vestibule and semicircular canals, 

 the cochlea being wanting. 



In fishes we have still the vestibular sac and mem- 

 branous semicircular canals, but the bone has not grown 

 completely about these so as to make bony cavities of 

 similar shape; nor are the cavities of the ear cut off 

 from the brain cavity. 



Finally in invertebrates the ear is reduced to a vestibu- 

 lar sac and otoliths. These, therefore, are the most fun- 

 damental and necessary parts of an organ of hearing. 



The hearing organs of invertebrates, however, are 

 much diversified in form and position. In insects they 

 are found sometimes in the first joint of the abdomen, as 

 in some grasshoppers; sometimes in the lower joint 

 (tibia) of the leg, as in other grasshoppers; and probably 

 sometimes in the antennas. Insects certainly hear, for 

 they produce sounds which are intended to be heard. 

 In all the cases above mentioned there is a hollow re- 



