112 THE LIFE-STORY OF INSECTS [CH. 



have been primitive among the Endopterygota, be- 

 lieving that the original environment of the larvae 

 of the ancestral stock of all these insects must have 

 been the interior of plant tissues. He is thus forced 

 to the necessity of suggesting that the campodeiform 

 larvae of ground-beetles or lacewings must be re- 

 garded as due to secondarily acquired adaptations ; 

 'they resemble Thysanura and the larvae of Hetero- 

 metabola only as whales resemble fishes.' There are 

 two considerations which render these theories unten- 

 able. The Neuroptera and Coleoptera among which 

 campodeiform larvae are common, are less specialised 

 than Lepidoptera,Hymenoptera,and Diptera, in which 

 they are unknown. And among the Coleoptera which 

 as we have seen (pp. 50 f.) display a most interesting 

 variety of larval structure, the legless, cruciform 

 larva characterises families in which the imago shows 

 the greatest specialisation, while in the same life-story, 

 as in the case of the oil-beetles (pp. 56-7), the newly- 

 hatched grub may be campodeiform, changing to the 

 cruciform type as soon as it finds itself within reach 

 of its host's rich store of food. 



A certain amount of difficulty may be felt with 

 regard to the theory of divergent evolution between 

 imago and larva, in the case of those insects with 

 complete transformation whose grubs and adults 

 live in much the same conditions. By turning over 

 stones the naturalist may find ground-beetles in 



