Modification of Development 173 



It has long been known that among the honey bees the 

 queen mother lays two kinds of c^gs: the unfertilized eggs 

 which develop into drones or males, and the fertilized q^^s 

 which develop into workers. These workers are females 

 in which the reproductive organs are not fully developed. On 

 the loss or death of the queen, a larva which would normally 

 develop into a worker is made to develop into a fertile female 

 by increasing the amount, and probably also modifying the 

 character, of the nourishment supplied. The fertile female 

 is certainly different from the unfertile worker; and this 

 difference results apparently from a difference in nutrition. 



Fig. 46. Influence of Thyroid on Development 



In each series, b shows the tadpoles that had been fed on thyroid much 

 more advanced in development, although smaller, than the controls, a. The 

 control animal in / was fed on plant food, in 2 on muscle, in j on adrenal. 

 All full size. The animals that were fed on thyroid developed very 

 rapidly, passing through the metamorphosis into the adult form while still 

 very small. Those fed upon thymus (not shown here) grew very rapidly 

 but failed to undergo their metamorphosis even after they had exceeded 

 the size of their parents. (After Gudernatsch.) From Gruenberg, Ele- 

 mentary Biology, published by Ginn & Company. 



Gudernatsch divided the fertilized eggs of a frog into 

 several sets of two batches each. When the tadpoles appeared 

 he supplied those in one batch with a special diet prepared 

 from the thyroid gland of a mammal, and he fed the others 

 with various foods. The thyroid gland has in recent times 

 become more familiar to us as the source of disturbances re- 

 lated to goiter, and of emotional manifestations related to 

 increased metabolism. Now Gudernatsch's tadpoles, who 

 presumably knew nothing about modern research into duct- 



