The Endocrine Glands - 415 



A * % 



ijm 



LARVA 



PUPA 



ADULT 



Fig. 22-9. Stages in life history of a Cecropia moth. See Figures 22-10 and 22-11, 

 and consult text (p. 414) in reference to the hormones that control these develop- 

 ments. 



so that finally a giant pupa and adult may be 

 produced. In the normal course of events, the 

 corpora allata temporarily become inactive, 

 soon after the last larval molt, whereupon a 

 normal sized pupa and adult comes into 

 being. 



In the pupa the complex reactions of meta- 

 morphosis are sustained by another impor- 

 tant hormone, the growth and differentiation 

 hormone (GDH). Recently this hormone has 



been isolated in pure form from silkworms 

 by two German workers, Karlson and Buten- 

 andt, although they have named it ecdysone, 

 since it also induces molting. GDH is pro- 

 duced by a pair of star-shaped masses of 

 glandular tissue, the prothoracic glands, 

 which lie in the anterior part of the thorax. 

 The prothoracic glands lie dormant until 

 they become activated by a trophic hor- 

 mone. This brain hormone is produced by a 



