STRUCTURE, GROWTH AND ECONOMICS OF INSECTS 



37 



Trichoptera, Coleoptera, Hymenoptera and Nematoceran Dipera; and 

 (3) coarctate in which the entire pupa is surrounded with a hardened 

 skin, and the appendages are not outwardly visible, e.g., higher Diptera 

 (Muscids, etc). 



Pupas are protected in different ways: (i) in puparia, (2) in earthen 

 cells in the ground, (3) in a rude cocoon in wood or earth, (4) in silken 

 cocoons, (5): in folded leaves, (6) as chrysalids. Examples of the 

 above types are everywhere about us. 



Internal Changes. — ^In the heterometahola the internal changes are 

 as direct as the external changes. In the holometabola, however, some 



Fig. 40. — Stages in the hypermetamorphosis of Epicauta. A, Triungulin; B, 

 carabidoid stage of second larva; C, ultimate stagejof second larva; D, coarctate 

 larva; E, pupa; F, imago. E is species cinerea; the others are vitlata. All enlarged 

 except F. {After Riley, from Trans. St. Louis Acad. Science.) 



of the larval organs are reconstructed into imaginal or adult tissues. 

 The imaginal organs arise from embryonal tissues (the imaginal buds) 

 which for the most part remain practically dormant in the larval stage; 

 in the pupal stage the purely larval organs disappear and the imaginal 

 organs continue their development. Histolysis is the term used to ex- 

 press the destruction of larval tissue by leucocytes, and histogenesis 

 for the construction of imaginal tissues. 



Imaginal Buds.—Th.e reproductive organs, the dorsal vessel, and 

 the nervous system gradually mature, but many of the organs develop 



