32 THE ORIGIN OF VERTIBRATES 
earliest fishes and members of the Paleostraca, the dominant race of 
arthropods which swarmed in the sea at the time: a similarity which 
could never have been suspected by any amount of investigation 
Fic. 16.—Bothriolepis. (After Parrsn.) 
An., position of anus. 
among living forms, but is immediately revealed when the ages 
themselves are questioned. 
I have not reproduced any of the attempted restorations of these 
old forms, as usually given in the text-books, because all such restora- 
tions possess a large element of fancy, due to the personal bias of the 
observer. I have put in Rohon’s idea of the general shape of Tre- 
mataspis (Fig. 17) in order to draw attention to the lamprey-like 
appearance of the fish according to his researches (cf. Fig. 18). 
Fic. 17.—Restoration oF Tremataspis. (After Rouow, slightly modified.) 
Fia, 18.—Ammoceetes. 
The argument, then, from geology, like that from comparative 
anatomy and from the consideration of the importance of the central 
nervous system in the upward development of the animal race, not 
only points directly to the arthropod group as the ancestor of the 
