INFLUENCE OF ENVIRONMENT 311 



oogenesis and spermatogenesis may lead to 

 the production of new races in the case of the 

 potato beetle (Fig. 94). I have found that a 

 slight increase in temperature at the time of 

 nuclear division may lead to abnormal 

 separation of the chromosomes and presum- 

 ably to a change in hereditary constitution; 

 Gager has obtained similar results following 

 the use of radium on plants. MacDougall's 

 experiments on plants point to the conclusion 

 that chemical substances may influence the 

 ovules so as to change the hereditary character 

 of the plant. Bardeen and the Hertwigs have 

 shown that great monstrosities may be pro- 

 duced if X-rays, radium or various chemical 

 substances are allowed to act on spermatozoa 

 before fertilization. Stockard subjected adult 

 male and female guinea-pigs to the fumes of 

 alcohol for some time before breeding them and 

 then studied the effects of this drug on their 

 offspring. He finds that the influence of alco- 

 hol on the spermatozoa is as deleterious as 

 when acting on the ova and that it produces 

 sterility, or greatly reduced fertility, a great 

 excess of still-births, and weak and sickly off- 



