THE EXTERNAL FORM OF WHALES n 



a vertically compressed tail. It is possible that we 

 may be justified in putting the question out of the 

 category of a "whale question" by adopting the 

 belief that whales have been derived from Sirenian- 

 like ancestors. 



Perhaps the ingenious Ray was nearer the truth 

 when he wrote that, "In Cetaceous fishes . . . the 

 tail hath a different position from what it hath in all 

 other fishes ; for whereas in these it is erected per- 

 pendicular to the horizon, in them it lies parallel 

 thereto, partly to supply the use of the hinder pair 

 of fins which these creatures lack, and partly to raise 

 and depress the body at pleasure. For it being 

 necessary that these fishes should frequently ascend 

 to the top of the water to breathe or take in and 

 let out the air, it was fitting and convenient that they 

 should be provided with an organ to facilitate their 

 ascent and descent as they had occasion." There can 

 indeed be no reasonable doubt but that this is an 

 important function of the whale's tail. It remains 

 under water for a long time until the air taken in by 

 respiration is exhausted ; it must then rapidly ascend 

 to the surface, perhaps from a great depth, to take 

 in a fresh supply. An air-breathing creature must 

 be in touch with the air. A powerful series of 

 strokes with the flukes would cause it to ascend 

 with great rapidity. But the Ichthyosaurus was also 

 an air-breathing creature, at least so we must assume 

 from its place in the class of reptiles ; it is, of course, 

 conceivable, even probable, that it may have possessed 

 accessory respiratory organs in the shape of vascular 



