170 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
fundamental features at least, the structural condition of the animal’s 
ancestors. Naturalists believe that all backboned or vertebrate 
Fic. 36.—Stages in the development of the prawn, Peneus potimirium. A 
Nauplius larva; B, first zoéa stage; C, second zoéa stage. (From Jordan and 
Kellogg, after Fritz Miiller.) 
we to 
Fic. 37.—Later stages in the development of the prawn, Peneus potimirium. 
D, Mysis stage; E, adult stage. (From Jordan and Kellogg.) 
