DEVELOPMENT 



137 



2. EXTERNAL METAMORPHOSIS 



Metamorphosis. One of the most striking phenomena of insect 

 life is expressed by the term metamorphosis, which means conspicuous 

 change of form after birth. The egg of a butterfly produces a larva; 

 this eats and grows and at length becomes a pupa; which, in turn, de- 

 velops into an imago. These stages are so different (Fig. 28) that with- 

 out experience one could not know that they pertained to the same 

 individual. 



Holometabola. The more specialized insects, namely, Coleoptera 

 (Fig. 206), Strepsiptera, Neuroptera, Mecoptera, Trichoptera, Lepi- 



FiG. 206. Cyllene caryce. A, larva; B, pupa; C, imago. X 3. 



doptera, Diptera (Figs. 207, 31), Siphonaptera (Fig. 32) and Hymenop- 

 tera (Fig. 287), undergo this indirect, or complete, 1 metamorphosis, 

 involving profound changes of form and distinguished by the internal 

 development of the wings and by a pupal stage that is usually inactive, 

 though active in mosquitoes and some midges, and in certain Neuroptera 

 just before the transformation. These insects are grouped together as 

 Holometabola. 



Larvae receive such popular names as "caterpillar" (Lepidoptera) , 

 "grub" (Coleoptera), and "maggot" (Diptera), while the pupa of a 

 moth or butterfly (especially the latter) is called a "chrysalis." 



These terms, though somewhat misleading in implication, are currently used. 



