H 



FLIES FOUND IN MOUSES 



jA 1 



W9 



Larva overfed, 

 pupation re- 

 tarded. 



Optimum, 

 60-72 houis. 



At the beginning of the change into the pupal state the body 



shortens by the withdrawal of 

 the anterior segments and 

 assumes a cylindrical shape, 

 the anterior and posterior 

 ends being evenly rounded. 

 In a few hours it assumes a 

 dark colour. 



" The larval skin forms the 

 pupal case or piipariiun in 

 which the larval organs under- 

 go disintegration and the 

 organs of the future fly are 

 built up." 



The mature fly or imago 

 escapes from the puparium by 

 pushing off the end of the 

 puparium by means of a 

 distensible bladder-like sac, 

 known as the ptilifium, which 

 protrudes from the forehead 

 of the emerging fly. When 

 the fly has crawled out of the 

 ruptured puparium the ptili- 

 num shrinks and is ultimately 

 retracted into the head of the 

 fl)% but a record of its exis- 

 tence is left in the form of a 

 crescent shaped scar, known 

 as the frontal Inuulc or suture, 

 which embraces the roots of 

 the antennae. When the fly 

 emerges its body is soft and 

 pale and its wings crumpled 

 (Fig. 10). In a short time 

 the cuticle hardens and the 



ir-^H 



60 hours 



hour.' 



4S liours. 



hours 



_^6 hours. 



Y\u. 12.— Illustrating the effect that under- 

 feeding the larva has on the size of the 

 adult fly [LttciHa aesar). Overfeeding, 

 if it does not result fatally, does not 

 increase the size of the fly over the 

 Optimum, as may he seen by the upper- 

 most individual, which is the same size 

 as the next lower individual or Optimum. 

 Each of the next lower individuals is the 

 result of decreasing the time of feeding 

 by six hours. These results are based on 

 a large number of individuals in each 

 case. 



wings become fully expanded. 

 After the cuticle has hardened the fl>^ grows no more. Young 



