Simplification and Complication 



21 



and good powers of flight. The eggs must, as a rule, be 

 laid a few together in carefully selected spots. The 

 larvae have little to do except to feed ; their limbs, sense- 

 organs, and even their mouth-parts become reduced or 

 lost, and the ultimate result may be a headless and foot- 

 less maggot. So great is the contrast between the larva 

 and the fly that an elaborate process of reconstruction is 

 necessary to effect the passage from one to the other. 

 The grub feeds voraciously, goes to sleep within the 

 hardened larval skin, and there undergoes a complete 

 renewal of all its organs and tissues, emerging as a fly, 

 which, in accordance with the difficulty of its task, is 



Fig. 12. — Larva of Corethra. ^ , dorsal view ; J5, side view, x 8. Tlie two pairs 

 of air-sacs are seen in tlie first and eighth segments behind the head. (From 

 Miall's Natural History of Aquatic Insects.) 



peculiarly active and gifted. A few insects may be 

 quoted to illustrate the progressive simplification of the 

 larva and the simultaneous complication of the fly. 



1. Corethra (fig. 12). — Larva active, carnivorous, with 

 prehensile antennae and mouth-parts. Larval head not 

 retractile ; eye-spots ; a tail-fin. No complete resting- 

 stage; the pupa lasts four to five days. Fly short-lived : 

 lays the eggs in a floating mass all together. 



2. Chlronomus. — Larva active, concealed, often feeding 

 on decaying vegetable matter. Larval head often small, 

 not retractile ; eye-spots and antennae distinct, though 



