ix] PAST AND PRESENT 111 



emerge to the upper air. Except for the possession 

 of tufted gills, adapting them to an aquatic life, the 

 stone-fly nymphs differ but slightly from the adults; 

 the grubs of the dragon-flies and may-flies, however, 

 are markedly different from their parents. In con- 

 nection with these comparisons, it is to be noted that 

 the dragon-flies and may-flies are more highly special- 

 ised insects than stone-flies, divergent specialisation 

 of the adult and larva is therefore well illustrated 

 in these groups, which nevertheless have, like the 

 Hemiptera and Orthoptera, visible external wing- 

 rudiments. 



From the vast array of insects that show internal 

 wing-growth and a true pupal stage, a few larval 

 types were chosen for description in Chapter vi, and 

 a review of these suggests again the thought of 

 increasing divergence between larva and imago. 

 Reference has been made previously to the many 

 instances in which the former has become pre-emi- 

 nently the feeding, and the latter the breeding stage 

 in the life-cycle. It seems impossible to avoid the 

 conclusion that the active, armoured campodeiform 

 grub differing less from its parent than an cruciform 

 larva differs from its parent, is as a larval type more 

 primitive than the caterpillar or maggot. A. Lameere 

 has indeed, while admitting the adaptive character of 

 insect larvae generally, argued (1899) with much 

 ingenuity that the cruciform or vermiform type must 



