AQUATIC MAMMALS 



that any equalization is necessary. There is no tension of the cetacean 

 tympanic membrane and hence no need for nice adjustments of pres- 

 sure within the ear to that of the auditory tube, such as is often so 

 annoying to us during speedy ascent of a mountain. No water, and 

 hence no pressure save that applied to the body surface can reach the 

 ear through the auditory tube. Judging by the powerful rush of the 

 air which leaves the cetacean blow hole as soon as the nasal orifice is 

 opened, the air is evidently retained between breaths at considerable 

 pressure greater than the external pressure when the body is at the 

 surface, and it seems that this air pressure must reach the inner ear 

 through the Eustachian tube, at least during the beginning of expira- 

 tion. It is therefore logical to assume that the inner ear has been simply 

 adjusted to withstand any pressure experienced without the necessity for 

 nice muscular adjustments for the equalization of pressure. 



OLFACTORY SENSE 



It is strikingly apparent that a mammal which seeks its food exclu- 

 sively beneath the surface of the water and comes to land only for brief 

 periods of basking or to have its young on some safe island retreat, from 

 whence it can dive into the water without an instant's delay, has vir- 

 tually no need for a sense of smell. Hence it is rather remarkable that 

 the Pinnipedia are so well equipped with olfactory apparatus. The ol- 

 factory bulbs are not as well developed as in most terrestrial carnivores, 

 according to O. R. Langworthy (MS), but the sense of smell is by no 

 means vestigeal in this order and turbinal bones of considerable com- 

 plexity are retained. It accordingly seems likely that a fairly well de- 

 veloped olfactory apparatus is a character which is not readily relin- 

 quished, at least by mammals of this sort, and that it will be retained 

 considerably after any great need for it has passed. 



Probably no mammal less specialized for an aquatic life than the 

 pinniped has had the olfactory apparatus appreciably reduced. In the 

 Sirenia it is considerably more reduced than in the Pinnipedia, and 

 Owen (1868) mentioned that the olfactory nerves are fewer and the 

 cribriform plates smaller in the dugong than the manati, as might be 

 expected from the greater aquatic specialization of the former. But 

 Murie (1872) stated that the size of the olfactory bulbs of the manati 

 indicates that its sense of smell is "fairly well developed." It is in the 

 Cetacea, however, than one finds the greatest olfactory alteration occur- 

 ring among aquatic mammals. The whalebone whales retain an ol- 

 factory apparatus, although it is vestigeal, but for what purpose it is 



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