302 



ZOOLOGY 



for example, only requires a few hours for hatching into the maggot stage. If food 

 and temperature are favorable, this maggot may grow to full size in a week, when 

 it passes into the resting or pupa stage, from which another week or more is required 

 for the young fly to emerge. 



The eggs of mosquitoes are deposited in water, where they hatch into active 

 larvae called " wigglers." These breathe the air by means of a tube on the next to 

 the last abdominal segment. Their common position with the end of the tail at 

 the surface of the water is thus explained. The mosquito larva does not cease 

 to be active, but by a series of moults comes to the pupa stage from which by an 



Fig. 142. 



Fig. 142. Stages in the development of the Bot-fly (ffaslrothilus equi). From Parker and 

 Haswell, after Brehm. a, adult insect; b, egg attached to a hair; c.d. and «, stages in the development 

 of the larva. (See also Fig. 141.) 



early moulting the adult mosquito emerges, balancing itself on the floating pupal 

 skin until its wings are hardened sufficiently for use. See Pig. 143. 



The Hessian-fly deposits its eggs on the leaves of growin|g wheat; certain of its 

 near relatives produce galls which interfere with the growth of the plant, often 

 very seriously. In the case of the Hessian-fly great damage to the wheat crop 

 often results. See Pig. 144. 



The fleas are to be looked upon as degenerate. They are often placed in a 

 separate order {Siphonaptera). The adults are external parasites without wings. 

 They are flattened laterally and thus pass readily between the hairs of the host. 

 The larvae are not parasitic, but live on decaying organic matter. 



