THE GENESIS OF SPECIES. 



[CHAP. 



have taken place in the comparatively short time occupied 

 by the evolution of these special fish forms, we might cer- 

 tainly expect other and far more bizarre structures would 

 (did not some law forbid) have been developed from other 

 rugosities, in the manifold exigencies of the multitudinous 

 organisms which must (on the Darwinian hypothesis) have 

 been gradually evolved during the enormous period inter- 

 vening between the first appearance of vertebrate life and 

 the present day. Yet with these exceptions, the position 

 of the limbs is constant from the lower fishes up to man, 

 there being always an anterior pectoral pair placed in front 

 of a posterior or pelvic pair when both are present, and in 

 no single instance are there more than these two pairs. 



MOUTH OF A WHALE. 



The development of whalebone (baleen) in the, mouth 

 of the whale is another difficulty. A whale's mouth is fur- 



