AQUATIC MAMMALS 



with the adipose cushion of other odontocetes, and that as it developed 

 in the more primitive Physeteridae it forced itself rearward between the 

 nasal passages. 



Be that as it may, the markedly posterior position of the bony nares 

 in the cachalot is suggestive, to me at least, that the blowhole of early 

 physeterids had receded almost as far to the rear as we now find it in 

 other odontocetes before the spermaceti organ had attained even mod- 

 erate size. In other words, in the sperm whale ancestors there was likely 

 a primary recession of the nares as in other odontocetes, but the sperma- 

 ceti organ forced a secondary migration of the spiracle in a forward di- 

 rection. But no fossil sufficently primitive to settle this point is yet 

 known. 



I think it is perfectly clear that this organ, developed to the pro- 

 portions which it now assumes in the sperm whale, cannot be a for- 

 tuitous modification. No animal would ever acquire such a cumbersome 

 contrivance which would be so great a handicap in swimming unless 

 there were definite physiological need for it. It may be, and probably 

 is, an overspecialization at the present time, its evolutional velocity out 

 of control, but it undoubtedly began in response to some definite need 

 which it now fulfills. It seems extremely unlikely that it has any pri- 

 mary function for the storage of a surplus of fat against periods of 

 food scarcity, for the animal is abundantly supplied with blubber, or 

 that it is used as an aid to the flotation of the head. But what the true 

 function of this remarkable organ may be is entirely unknown. 



[106] 



