NO. 6 



CATERPILLAR AND BUTTERFLY — SNODGRASS 



39 



moth or butterfly. The newly developing adult takes whatever parts of 

 the larva can be utilized with adaptive modifications, such as the heart, 

 the tracheae, and the nervous system. Otherwise it is a new creature 

 built up from imaginal cells that have remained undifferentiated 

 during the life of the larva, while the unused parts of the larva are 

 cast off or go into dissolution within the pupa. As already noted, 

 some adult organs may begin their development in an early instar 

 of the larva. 



mxPrb" 



ft] A 



B 



Fig. 17. — Examples of moths with and without a proboscis. 



A, Head of peach borer moth, Sanninoides exitiosa, with fully developed 

 maxillary proboscis. B, Tent caterpillar moth, Malacosoma americanum, with 

 greatly reduced maxillae, no organs of feeding. 



Lb, labium; IbPlp, labial palpus; Mx, maxilla; mxPrb, maxillary proboscis. 



The interior of a lepidopterous pupa is filled with what appears to 

 be a thick creamy substance. Under the microscope it is seen to consist 

 of a clear, pale, amber-yellowish liquid containing a mass of minute 

 bodies, some of which are blood cells and phagocytes, but most of 

 them are disintegrating fat cells and liberated granules and fat drop- 

 lets. The principal structural changes that take place within the pupa 

 of a moth or butterfly affect the musculature, the fat tissue, and the 

 alimentary canal. 



The transformation of the muscular system differs in degree in 

 different insects according to the difference in the musculature of the 

 larva and the adult. Some larval muscles go over unchanged into the 

 adult, others undergo a certain amount of reconstruction without 

 losing their identity, and still others that are specifically larval muscles 



