AQUATIC MAMMALS 



iological need. What this function can be is entirely unknown, but it 

 it only logical to presume that as specialized fat organs such as are being 

 discussed occur only in the Cetacea they have something to do with the 

 ability of this order either to hold the breath for a phenomenal length of 

 time, or to assist in withstanding great pressures an explanation which 

 seems unlikely. 



In what way could this oil system of the narwhal assist the animal to 

 hold its breath? The only possibility that occurs to me is that there 

 might be sufficiently close connection between capillaries of the oil sys- 

 tem and vascular capillaries for there to be possible interchange of car- 

 bon dioxide by diffusion. The process then would be for the oil to take 

 over a part of the carbon dioxide as this accumulated in the blood dur- 

 ing prolonged submergence. When at the surface once more some eight 

 or ten breaths might then enable the oil to give up its excess of carbon 

 dioxide by the same process reversed. And it is well known that after a 

 lengthy submergence a whale must spend an approximately equal period 

 of time at the surface, frequently inflating the lungs, before it can again 

 repeat its dive. The above is a possibility, I say, but it should be 

 emphasized that it is not probable and it is offered merely as the only 

 explanation that presents itself. 



If this detail of the narwhal has been developed to facilitate long sub- 

 mergence one would naturally suppose that this animal can remain be- 

 low the surface for a longer period than can the majority of porpoises, 

 but it is not known whether this is actually the case. It appears only 

 reasonable, however, that cetaceans of the order of the narwhal and be- 

 luga which occur where they must often be hemmed in by extensive ice 

 fields should have unusual ability for lengthy submergence, and it will 

 be of interest to ascertain whether the latter has also developed this oil 

 system. 



The sperm whale or cachalot is believed to have the ability to sub- 

 merge for a longer period than any other cetacean, and it is the only one 

 which has developed a spermaceti organ of phenomenal size. I am 

 unable to believe that these two circumstances have no connection, but 

 there is no clue to the manner in which they may be dependent. The 

 fact that the fatty equipment of the narwhal and cachalot are so very 

 different may be without much significance, for they were undoubtedly in- 

 dependently developed and could fulfill the same need. The difficulty 

 lies in the statement that the spermaceti organ is a "closed system," and 

 no mention is made of any marked vascular networks. 



Through the efforts of H. C. Raven and H. I. Wordell I secured two 



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