PARTS AND FEATURES 



brain are its large cerebellum, and the fact that it is larger in transverse 

 than in sagittal measurement, the latter feature undoubtedly being a re- 

 flection of the peculiar skull development. 



FATTY TISSUES 



It has already been remarked that aquatic mammals are particularly 

 prone to develop fatty tissue of one sort or another. An extensive blub- 

 ber layer irrefutably fulfills a physiological need in aiding the retention 

 of body heat by those sorts which inhabit cold waters. This does not 

 apply with equal force to tropical and subtropical sirenians and cetaceans. 

 Apparently they could make other provision for withstanding the very 

 moderate temperatures to which they are subjected, and yet in spite of 

 their abundant fat the former are particularly susceptible to any slightly 

 unusual chilling of their aquatic habitat. It thus seems not unlikely that 

 the blubber layer may have other uses than purely that of insulation. 



Seals, at least, often have a great deal of intestinal fat, and the Odonto- 

 ceti usually have accessory fatty equipment in the form of a frontal 

 adipose cushion of a specialized quality of fat, and other deposits about 

 the angle of the jaw. Of greater significance still is the enormous and 

 unwieldly spermaceti organ of the cachalot, and what I have previously 

 referred to as a sort of circulatory system for oil. This, apparently, is 

 present to a very slight degree in the porpoise Neomeris, but has not 

 been reported in other cetaceans. In a fetal narwhal (Monodon), how- 

 ever, which I dissected, the subcutaneous tissue, and much of the inter- 

 muscular tissue, was given the appearance of a rubber sponge by an 

 amazingly intricate and extensive system of oil ducts, intercommunicat- 

 ing with each other and with larger subcutaneous oil reservoirs. Even 

 some of the larger muscles had small oil sinuses throughout their sub- 

 stance. About the neck at least these oil ducts were very numerous, of 

 very small diameter, and apparently had intimate relation with the retia 

 of the vascular system. How extensive the flow of oil through these 

 ducts from one part of the body to another may be in the live animal 

 is of course unknown, but while dissecting the back, if one pressed upon 

 the dorsal region oil welled up and out in copious amount. In life mus- 

 cular pressure could attain the same result, and there would accordingly 

 be an irregular, and possibly somewhat limited, flow of oil from one 

 area to an adjoining one. 



This specialization of the narwhal cannot be fortuitous any more than 

 can the spermaceti organ of the cachalot. Any such unique and strongly 

 marked character must have been developed to fulfill some definite phys- 



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