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. 
