SENSES, INSTINCTS, AND INTELLIGENCE 329 



ear-trumpet. That the comphcation should occur in owls 

 may be associated with the nocturnal habits of these birds. 

 Mr. Beebe suggests that the movable flap may help the owl 

 in focussing the sounds made by mice and other small 

 booty on the ground. In the courtsliip dance of the cock 

 capercailly the ear is blocked for a brief moment at the climax 

 of the excitement by the swelling up of an erectile fold in 

 the outer ear-passage. 



The short outer ear-passage (external auditory meatus) 

 has stretched across it as usual the drum or tympanum, 

 which made its first appearance in amphibians. From this 

 taut membrane, which vibrates as the waves of sound strike 

 it, the vibrations pass down a delicate rod or columella 

 whose expanded inner end abuts on a window (fenestra 

 ovalis) into the internal ear, the proper organ of hearing, 

 which is lodged in the recesses of the periotic bone. The 

 vibrations conveyed by the columella affect the fluid in 

 the inner ear, and through that medium the hair-like 

 endings of the auditory nerve. 



The story of the Capitol geese is typical of many records 

 of the quick sense of hearing in birds. This is confirmed 

 by everyday observation, but it is noteworthy that many 

 birds are very indifferent to loud noises, such as those of 

 a passing locomotive or a bursting shell. As with other 

 creatures, attention is paid to sounds which interest either 

 inborn equipment or acquired associations. Too much 

 must not be made of the argument that birds must have a 

 keen sense of hearing because many of them are fine song- 

 sters, for one is reminded that many insects are very skilful 

 instrumentalists and yet we know almost nothing in regard 

 to the sense of hearing in insects. 



Around the main chamber of the inner ear lie the three 

 semicircular canals, in three different planes. They con- 

 tain fluid and there are very numerous nerve-endings where 

 they join the main chamber. Experiments show that 

 they have a balancing or equilibrating function, and it is 

 interesting to remember that this, and not hearing, is the 

 chief use of the ear in backboneless animals. When all 



