DEVELOPMENT 183 



of the details of the internal metamorphosis in Lepidoptera 

 have been described by Newport and Gonin. Figure 223, 

 after Newport, shows some of the more evident internal dif- 

 ferences in the larva, pupa and imago of a lepidopterous insect. 

 Significance of Pupal Stage. To repeat among holo- 

 metabolous insects the function of nutrition becomes relegated 

 to the larval stage and that of reproduction to the imaginal 

 stage. Larva and imago become adapted to widely different 

 environments. So dissimilar are the two environments that 

 a gradual change from the one to the other is no longer pos- 

 sible ; the revolutionary changes in structure necessitate a tem- 

 porary cessation of external activity. 



