290 



EVOLUTION AND GENETICS 



data on the Orthoptera show striking chromosomal similarity 

 among related species of these insects. 



The entire body of facts relating to chromosomal behaviour is 

 so significant that it has given rise to the chromosomal theory 



-.1,. I, -,->j;i«-^ 



C D 



Fig. 167. — Various cells. A, from peritoneum of salamander; 5, spermato- 

 gonium of frog; C, spinal ganglion cell of frog; D, spermatocyte of Proteus, 

 nucleus in spireme stage. (From Wilson, A after Flemming, B and D after 

 Hermann, C after Lanhossek.) 



of heredity which postulates that these minute bodies are the 

 seat of the substances or particles which are handed down from 

 one generation to the next as the foundation of hereditary resem- 

 blance. 



