244 



GENERAL BIOLOGY 



beetle Psephenus lecontei) and the larva of the netwinged 

 midge (Blepharocera) to be compared as to form of body, 

 adapted to clinging to rocks) : or, 3) in similar rapid waters, 

 the immature stages of mayflies of the genus Heptagenia 



FIG. 151. Photograph of a fossil dragonfly in the Museum of Comparative 

 Zoology at Cambridge, Mass. 



and 6f stoneflies of the genus Perla. 



A special phenomenon of parallelism, affecting more 

 superficial characters will be studied in chapter VI under 

 the name of mimicry. 



