INFLUENCE OF ENVIRONMENT 315 



heredity and environment in development be 

 determined. Extensive experiments have 

 been made within recent years on developing 

 animals and plants in order to discover the 

 factors involved in development, and the modi- 

 fications which may thus be produced are very 

 striking. 



B. EXPERIMENTAL MODIFICATION OF 

 DEVELOPMENT 



The study of development under experi- 

 mental conditions has given rise to a new 

 branch of biology, viz., experimental embry- 

 ology or the physiology of development. By 

 changes in environmental conditions notable 

 modifications may be produced in adult or- 

 ganisms, but these modifications are much 

 greater when the changed environment acts 

 on the organism during the period of its de- 

 velopment. 



I. Developmental Stimuli 



It is by no means easy to define such gen- 

 eral terms as "environment," "stimulus," "re- 

 sponse." In its common use "environment" 



