Evolution of Fishes from Invertebrates 95 



rocks. But it can be asserted with entire confidence that 

 the primitive Silurian fishes undoubtedly sprang from some 

 ancestral invertebrate types of more archaic build. And the 

 metanemerteans are the only organisms which, not merely 

 in superficial aspect, but in minute structural detail, fulfill 

 the requirements of the case. Vigorous and continued in- 

 vestigation therefore of all available material, at all stages 

 in their life-history, will yield results of highest evolutionary 

 importance. 



