28 



AN INTRODUCTION TO ENTOMOLOGY 



rudimentary (Fig. 38). But in other orders of insects the immature 

 forms have been greatly modified to adapt them to special modes of 

 life, with the result that they depart widely from the insect type. For 

 example, the larv^ai of bees, wasps, flies, and many beetles are legless 

 and more or less worm-like in form (Fig. 4) ; while the larvae of butter- 

 flies and moths possess abdominal as well as thoracic legs (Fig. 39). 



Fig- 39- — A larva of a handmaid moth, Datana. 



Although the presence of wings in the adult state is characteristic 

 of most insects, there are two orders of insects, the Thysanura and 

 the Collembola, in which wings are absent. These orders represent 

 a branch of the insect series that separated from the main stem before 

 the evolution of wings took place; their wing- 

 less condition is, therefore, a primitive one. 

 There are also certain other insects, as the lice 

 and bird-lice, that are wingless. But it is 

 believed that these have descended from 

 winged insects, and have been degraded by 

 their parasitic life; in these cases the wingless 

 condition is an acquired one. Beside these 

 there are many species belonging to orders in 

 which most of the species are winged that 

 have acquired a wingless condition in one or 

 both sexes. Familiar examples of these are the 

 females of the Coccidse (Fig. 40), and the 

 females of the canker-worm moths. In fact, 

 wingless forms occur in most of the orders of 

 winged insects. 



As the structure and transformations of insects are described in 

 detail in the following chapters, it is unnecessary to dwell farther on 

 the characteristics of the Hexapoda in this place. 



Fig. 40. — A mealy-bug, 

 Dactylopius. 



