COCOON, PUPA, AND MOTH 19 



In this shape the pupa lies until its time comes 

 to let loose the imago — the moth. But before this 

 time comes many changes have occurred within the 

 brown pupa-skin. All the old organs which were 

 necessary to the crawling, voracious caterpillar, but 

 are not needed by the moth, must be destroyed, and 

 this destruction is accomj)lished by the plmg'ocytes, 

 or lymph-corpuscles. The unnecessary organs are 

 weakened from ceasing to perform the functions which 

 they did perform in the caterpillar, and therefore are 

 easily destroyed by the phagocytes, while the imaginal 

 buds which are to grow into organs needed by the 

 moth — and such organs as perform their functions 

 during the changes from caterpillar to moth — are too 

 strong to be harmed by the phagocytes, and are 

 thought to be nourished by them. Such destruction 

 of unneeded organs occurs in the caterpillar stage as 

 well as in the pupa stage. It is probable that when- 

 ever a tissue or organ becomes unnecessary it is 

 destroyed in this way. Investigations have shown 

 that the organs of the moth are not fully developed in 

 the pupa until it is nearly time for the moth to emerge, 

 but the development is rapid when it once begins. 



Some puppe have special organs which help emer- 

 gence. Bryocampa ruhicimda, a pupa formed under- 

 ground, has on its abdominal segments, at almost 

 right angles to the body, rows of spines which keep 

 the pupa from slipping back while working its way to 

 the surface of the earth. The pupa must come to the 

 surface because the soft, moist moth would be unable 

 to make its way through the earth without injury. 

 The pupa of Cressoiilajuglandis has two points on the 



