112 The Life-History of Insects 



through the soil in search of food. The presence of 

 an abundant food supply obtainable without exertion 

 is always correlated with the degraded form of larva 

 to which the term "maggot" is applied — no feet, 

 and often no chitinised head-capsule 

 with its special sense organs. Such 

 maggots are the offspring of insects 

 which lay their eggs in a mass of food- 

 material, as the Blowfly, or which care- 

 fully tend and feed their young, as the 

 Wasps. In the case of a few degraded 

 parasitic flies, the whole larval life is 

 passed within the body of the mother, 

 and the insect is only born in the stage 

 preceding the perfect condition (67, 



71, 72). 



Aquatic Larvse. — In a large 

 number of insects the larval and nym- 

 phal stages are spent in the water. 

 Aquatic larvae, like those which live 

 on the land or burrow in the soil, 

 may be vegetarians, flesh-eaters or 

 scavengers. Their peculiar interest 

 lies in their method of breathing. 

 The usual air-openings (spiracles) are 

 necessarily closed against the ingress 

 of water. Many aquatic grubs breathe 

 the air dissolved in the water by means 

 of leaf-like gills through which run 

 branching air-tubes. Stone-fly and 



Fig. 71.— Nymph of 

 May - fly (Chloeon 

 di/>tcrum), with 

 wing-rudiments (a) 

 and tracheal gill- 

 plates (^ iJ.). Mag- ■f.ir n - ■> r • ^ 



nified 7 times. From May-fly grubs, tor mstauce, possess 



(fft^e" VaySfe"e)^ pairs of such tracheal gills on several 



Ss\rI"urshorT]' Segments of the body (fig. 71). In 



the Alder-fly grub, the paired tracheal 



gills are tubular and jointed, and the tenth segment of 



the hind-body is lengthened out into a fringed ** tail," 



