THE SENSES 



distance until it is sealed entirely, once more becoming open and again 

 expanding farther proximad. 



It is usually stated in the literature that auricular musculature has 

 disappeared entirely in the Odontoceti, and is vestigeally represented by 

 one or two remnants in the Mysticeti, but few investigators have spec- 

 ialized sufficiently in the facial musculature to do a thoroughly satis- 

 factory dissection of this portion of the Cetacea. A slip, believed to be 

 a vestige of the ear muscles, was found by me in Neomeris but because 

 of the bad condition of the specimen I could not be positive. Ernst 

 Huber has found remnants of several auricular muscles in the narwhal, 

 and I confidently expect that there are actually more than the two usu- 

 ally stated to occur in mysticetes. A vestige of the auricular cartilage 

 has also been found in some whales. 



It is extremely doubtful if any aquatic mammal swims with the audi- 

 tory tubes open. Hence, as the tube is closed when beneath the water 

 a mammal can use its ear in normal manner only for air-borne sounds. 

 Thus the ears of a mink or beaver are probably largely inoperative un- 

 der water save as sound waves may be transmitted by resonance through 

 parts of the head. When, in an aquatic mammal, the opening me- 

 chanism of the ear has ceased to function and the lumen remains closed, 

 normal use of the ears will cease forever, for then neither air nor water 

 can transmit extraneous sounds directly to the ear drum. The latter 

 situation now obtains in the Cetacea. But there must be a gradual ac- 

 commodation to this change a gradual increase in ability to receive 

 water borne vibrations and a gradual decrease in the power to receive 

 those transmitted by air. And there must be a change in the quality of 

 reception also, for it is unthinkable that during the thousands of years 

 since the abandonment of atmospheric hearing in the Cetacea they re- 

 ceive sounds under water only after the same fashion as do we when the 

 head is submerged. It is not unlikely that the Pinnipedia are now un- 

 dergoing this auditory alteration, and that the change is more marked in 

 the Sirenia. 



There is abundant evidence that whales are sensitive to certain water 

 borne vibrations which cannot possibly be transmitted through their 

 auditory or Eustachian tubes. Hence these waves must be transmitted 

 through some solid part of the head, but we have no means of ascer- 

 taining which part is most resonant. There is further proof of ceta- 

 cean keenness of hearing in the high development of the internal ear, 

 and in the size and character of the acoustic colliculus, which in a por- 



[71] 



