PHYLUM ARTHROPODA 



237 



are not necessarily carried over directly into the following stage. 

 Many of the larval organs disappear as a result of phagocytic 

 or chemical action, and through histogenesis new organs of the 



A * c 



Fig. 112. — Development of a holometabolous insect. A, larva; B, puparium; 

 C, imago of fly {Phormia regina) . {From Folsom's Entomology, courtesy of P. 

 Blakiston's Son and Co,). 



adult are formed. In the Holometabola, wings and legs of the 

 adult do not develop externally on the larva but develop inter- 



FiG. 113. — Development of a heterometabolous insect. Six successive 

 instars of the squash bug, Anasa tristis. A to E, nymphs; F, adult or imago. 

 (From Folsom,'s Entomology, courtesy of P. Blakiston's Son and Co.). 



nally as imaginal buds (Fig. 126) which emerge and become free 

 only later in development. 



The Heterometabola include those insects which transform 

 without a true pupal period. The stages between the egg and 



