DEVELOPMENT 



179 



FIG. 219. 



condition. In accounting for the evolution of metamorpho- 

 sis, the theory of natural selection 

 finds one of its most important appli- 

 cations. 



3. INTERNAL METAMORPHOSES 



In Heterometabola, the internal 

 post-embryonic changes are as di- 

 rect as the external changes of 

 form; in Holometabola, on the con- 

 trary, not all the larval organs 

 pass directly into imaginal organs, 

 for certain larval- tissues are de- 

 molished and their substance recon- 

 structed into imaginal tissues. When 



FIG. 220. 



Diagrammatic transverse 



section of Corethra larva, to 

 show imaginal buds of wings 

 (a/) and legs (/) ; h, hypoder- 

 mis; i, integument. Modified 

 from Lang's Lelirbucli. 



Diagrammatic transverse sections of muscid larvse, to show imaginal buds, h, lar- 

 val hypodermis; i, larval integument; Hi, imaginal hypodermis; /, imaginal bud of 

 leg; w, imaginal bud of wing. Modified from Lang's Lehrbuch. 



