138 



ENTOMOLOGY 



Heterometabola. In a grasshopper, as contrasted with a butterfly, 

 the imago, or adult, is essentially like the young at birth, except in hav- 

 ing wings and mature reproductive organs, and the insect is active 

 throughout life, the wings developing externally; hence the meta- 

 morphosis is termed direct, or incomplete. This type of transformation, 



without a true pupal period, is 

 characteristic of the more gener- 

 alized of the metamorphic insects, 

 namely, Orthoptera, Dermaptera, 

 Platyptera, Plecoptera (Fig. 19), 

 Ephemerida (Fig. 20), Odonata 

 (Fig. 2 1) , Thysanoptera and Hemi- 

 ptera (Fig. 208). These orders 

 constitute the group Heterome- 

 tabola. Within the limits of the 

 group, however, various degrees of 

 metamorphosis occur; thus Plec- 

 PIG. 2<>7.Phormia regina. A, larva; B, opteraj Ephemerida and Odonata 



undergo considerable change of 

 form; a resting, or quiescent, period may precede the imaginal stage, 

 as in Cicada (Fig. 209) . In fact, the various kinds of metamorphosis 



PIG. 208. Six successive instars of the squash bug, Anasa tristis. X 2. 



grade into one another in such a way as to make their classification to 

 some extent arbitrary and inadequate. 



As there is no distinction between larva and pupa in most hetero- 



