1 84 CLUES AND SUGGESTIONS CHAP. 



of that line of adaptation it is really not 

 much of a puzzle that one particular 

 element in the vertebrate skeleton should 

 be passed over and left, as it were, aside, 

 because it is a part of the original plan 

 which could be of no service here. 

 There is no rational ground for suppos- 

 ing that this particular bit of internal 

 structure must necessarily have been 

 developed into functional use in some 

 former terrestrial progenitor. Organic 

 beings are full of structures which are 

 variously used, and of others which are 

 so embryonic that they can never have 

 been of any use at all. On the other 

 hand, it is a very violent supposition that 

 the external structure of the Whale can 

 ever have been inherited from a terres- 

 trial beast by the normal processes of 

 ordinary generation. The changes are 

 not only too enormous in amount, but 

 too complicated in direction, to lend 



