AQUATIC MAMMALS 



Also in trying to explain the asymmetry of the skull in toothed whales 

 Kiikenthal (1908) made the claim that the flukes are asymmetrical. He 

 was led to this belief because in many of the embryos which he examined 

 the caudal lobes were set somewhat awry, and from this he argued that 

 a similar condition in the tails of baleen whales was accompanied by 

 slight though recognizable asymmetry in the mysticete skull. His thesis 

 was that an asymmetrical tail, used in sculling movements, tends to turn 

 the animal to the left, when the unequal pressure of the water upon the 

 two sides of the head will have resulted, throughout long ages, in an 

 asymmetrical skull. At the present time this theory is given very slight 

 credence. It is true that Kiikenthal figured the transected tail of a ror- 

 qual which showed the flukes in somewhat oblique relation to the verte- 

 brae, but even if this accurately depicted the conditions in life this in- 

 dividual may have been pathological. The caudal conditions in pre- 

 served embryos are entirely without significance, for the preservative act- 

 ing upon soft tissue in a cramped position invariably distorts the flukes, 

 and almost always they will remain fixed in the shape of an S. I have ex- 

 amined numerous cetaceans, both odontocetes and mysticetes, with pos- 

 sible asymmetry of the tail in mind and have never found the slightest 

 indication of such being the case. 



Ray seems to have been the originator of the belief that the horizontal 

 direction of the whale's flukes was attained because the animal is an air- 

 breather, and such provision enables it more easily to seek the surface 

 for a fresh breath. In the literature this is often repeated without com- 

 ment. A little reflection, however, will convince one that there can be 

 nothing to this reasoning, as Beddard (1900) and a few others seem to 

 have concluded. In the first place no such function as ease of ascent 

 from great depths could have had the slightest influence upon the ini- 

 tial stages of tail change in the cetacean ancestor. Caudal development 

 must have started in conformity with the manner of swimmng then em- 

 ployed without regard to any final use to which the tail would be put. 

 In the second place, when the tail is used as the primary means of pro- 

 pulsion it will become specialized so as to drive the animal forward in 

 a straight line, regardless of the direction of flattening, while other de- 

 tails of the body will take over the function of steering. At speed the 

 whale evidently elevates or depresses its line of progress by the flippers 

 alone, save in the case of an abrupt turn, and it could with the greatest 

 ease swim either straight up or straight down were the flukes vertical 

 instead of horizontal. 



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