No. I.] THE VERTEBRATE EAR. 319 



be made to serve in place of the higher sense organs for the 

 orientation of the body, we may take the nasal sensory appara- 

 tus of the common mole (Eimer, 79, 1871), or, better still, that 

 of the star-nosed mole {Condyhwa cristatd). I have described 

 in another place (6, 1885), the unusual nasal rays of this animal. 

 This remarkable tactile apparatus is undoubtedly produced in 

 response to needs of the animal, owing to its practical loss of 

 sight, and it serves admirably to orient the body in the subter- 

 ranean passages in which this mole lives. 



Many more such facts might be brought forward to strengthen 

 the view that the equilibration of the body is the product of the 

 total of the activities of the nervous system acting over the 

 whole periphery of the body, and is not the result of the activity 

 of any special organ or group of organs such as the semicircular 

 canals. 



37. The filaments of the hair band meet the physical require- 

 ments of acoustics for the perception and transmission of the 

 "waves" of auditory stimuli. 



38. Timbre or the tonal color of sounds is due to a combina- 

 tion of the stimuli or the effects of the excitation of a series of 

 vibrations of which the main or fundamental tone is most promi- 

 nent, while the other vibrational impulses make themselves felt 

 as "coloring" of this base. The combination is a psychical 

 phenomenon, and there is no combined result of simultaneous, 

 sympathetic vibrations transmitted from the ear ; on the con- 

 trary, each vibrational impulse is transmitted to the brain at its 

 full value, and its effect in audition is due entirely to psychical 

 processes. 



39. In the dog, according to Foster, the average pressure in 

 the cerebro-spinal fluid is equal to 10 mm. of mercury, i.e. about 

 one-tenth to one-seventeenth of the carotid pressure ; and since 

 the cerebro-spinal spaces com.municate with the auditory chan- 

 nels (even though indirectly), this degree of pressure must be 

 very near that under which the structures of the internal ear are 

 called upon to carry out their functions, — a physical condition 

 which should be kept in mind while dealing with the physiology 

 of the ear sense organs in the Mammalia. 



40. The function of the cochlea is carried out by the hair 

 cells of the cochlea, which bear the long, slender, percipient hairs 

 in such fashion that the waves of the endolymph are readily 



