326 



HEREDITY AND ENVIRONMENT 



action of unusual environmental stimuli dur- 

 ing later stages of development. Gudernatsch 

 found that if tadpoles of the frog were fed on 

 the thyroid gland they transformed into 

 minute frogs, scarcely larger than flies, but if 

 fed on thymus gland they grew to be large, 

 dark colored tadpoles but did not change into 

 frogs; if fed on the adrenal gland they pro- 

 duced extremely light colored forms. If canary 

 birds are fed on sweet red pepper they become 

 red in color. If the larvae of bees are fed on 

 "royal jelly," which is a bee food rich in fats, 

 they become fertile females or queens; if fed 

 on ordinary "bee bread" they become infertile 

 females or workers (Fig. 79). There are 



Fig. 79. The three castes of the honey bee. A, worker or 

 imperfect female, B, queen or perfect female, C, drone or 

 male. The differences between workers and queens are pro- 

 duced by the type of food supplied to the larvse, 



