42 



THE GENESIS OF SPECIES. 



[CHAP. 



all these fishes the two eyes, which in the young are 

 situated as usual one on each side, come to be placed, in 

 the adult, both on the same side of the head. If this 

 condition had appeared at once, if in the hypothetically 

 fortunate common ancestor of these fishes an eye had 

 suddenly become thus transferred, then the perpetuation 

 of such a transformation by the action of " Natural Selec- 

 tion " is conceivable enough. Such sudden changes, haw- 

 ever, are not those favoured by the Darwinian theory, and 

 indeed the accidental occurrence of such a spontaneous 



PLEtlRONECTIDJE, WITH THE PECULIARLY PLACED EYE IN DIFFERENT POSITIONS. 



transformation is far from probable. But if this is not so, 

 if the transit was gradual, then how such transit of one 

 eye a minute fraction of the journey towards the other side 

 of the head could benefit the individual is indeed far from 

 clear. It seems, even, that such an incipient transforma- 

 tion must rather have been injurious. Another point with 

 regard to these flat-fishes is that they appear to be in 

 all probability of recent origin i.e. geologically speaking. 

 There is, of course, no great stress to be laid on the mere 



