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 Paldostraca 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 paleeostracan 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 
Fis, Gi Anos Yoni fhe. Hayat closely than the fish of a later era. 
Natural History). Dorsal view. 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- 
Fic. 10.—Branchipus stagnalis. (From Cuavs.) 
ance are the two groups of animals, so different their methods of 
locomotion, that it is apparently only an inmate of a lunatic asylum 
