28 



THE ORIGIN OF VERTEBRATES 



arthropod-like animals which gave origin to the trilobites themselves. 

 This name I shall adopt, and speak, therefore, of the Palasostraca as 



the dominant race at the time when 

 vertebrates first appeared. 



If, then, there is no break in the 

 law of evolution here, the race which 

 was predominant at the time when 

 the vertebrate first appeared must 

 have been that from which the first 

 fishes arose, and these fishes must 

 have resembled, not the crustacean 

 proper, or the arachnid proper, but a 

 member of the palreostracan group. 

 Moreover, just as the Labyrinthodonts 

 show special affinities to the fishes 

 which were then living, so we should 

 expect that the forms of the earliest 

 fish would resemble the arthropodan 

 type dominant at the time more 

 closely than the fish of a later era. 



At first sight it seems too great 

 an absurdity even to imagine the 

 possibility of any genetic connection between a fish and an arthropod, 

 for to the mind's eye there arises immediately the picture of a 

 salmon or a shark and a lobster or a spider. So different in appear- 



Fig. 9. — Apus (from the Royal 

 Natural History). Dorsal view. 



Fig. 10.— Branchipus stagnalis. (From Claus.) 



ance are the two groups of animals, so different their methods of 

 locomotion, that it is apparently only an inmate of a lunatic asylum 



