OUR FACE FROM FISH TO MAN 



moving in a fore-and-aft direction and building up 

 a complex head through the fusion of simple seg- 

 ments, yet the arthropods developed their jaws 

 out of jointed locomotor appendages while the 

 vertebrates utilized for this purpose the cartilagi- 

 nous bars of the first two gill pouches. According 

 to Patten's view the fossil ostracoderms (Fig. 4) 

 were more or less intermediate between these two 

 great groups; but the objections to this view are 

 formidable. 



No matter from what group of invertebrates the 

 vertebrates may have sprung, their origin took 

 place many hundreds of millions of years after the 

 first synthesis of living matter from less complex 

 substances. When the first fishes took form the 

 seas already swarmed with thousands of species 

 of marine invertebrates, — protozoans, sponges, cor- 

 als, trilobites, crustaceans, brachiopods, arthro- 

 pods, molluscs, etc., and so far as the marine inver- 

 tebrates were concerned, all the major problems 

 of feeding, locomotion, sexual and asexual repro- 

 duction had been solved aeons ago. And when the 

 vertebrates started on their long career they too 

 had already solved all the same fundamental prob- 

 lems by rigorously sacrificing much of their old 



