44 THE GENESIS OF SPECIES. [CHAP. 



priate action, which is against the hypothesis. Again, the 

 change from mere indefinite and accidental processes to 

 two regular pairs of symmetrical limbs, as the result of 

 merely fortuitous favouring variations, is a step the feasi- 

 bility of which hardly commends itself to the reason, seeing 

 the very different positions assumed by the ventral fins in 

 different fishes. If the above suggestion made in opposition 

 to the views here asserted be true, then the general con- 

 stancy of position of the limbs of the Vertebrata may be 

 considered as due to the position assumed by the primitive 

 rugosities from which those limbs were generated. Clearly 

 only two pairs of rugosities were so preserved and developed, 

 and all limbs (on this view) are descendants of the same 

 two pairs, as all have so similar a fundamental structure. 

 Yet we find in many fishes the pair of fins, which corre- 

 spond to the hinder limbs of other animals, placed so far 

 forwards as to be either on the same level with, or actually 

 in front of, the normally anterior pair of limbs ; and such 

 fishes are from this circumstance called " thoracic " or 

 "jugular" fishes respectively, as the weaver fishes and the 

 cod. This is a wonderful contrast to the fixity of position 

 of vertebrate limbs generally. If then such a change can 

 have taken place in the comparatively short time occupied 

 by the evolution of these special fish forms, we might 

 certainly expect that 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 enor- 

 mous period intervening between the first appearance of 

 vertebrate life and the present day. Yet, with these excep- 

 tions, the position of the limbs is constant from the lower 



