THE PROBLEMS OF TRANSFORMATION 251 



increasing divergence between imago and larva the resting 

 pupal stage becomes essential so as to give opportunity for 

 the necessary disintegration of larval tissue and the recon- 

 struction of the organs of the winged insect from the imaginal 

 buds. 



But if this general conclusion is plain, there remain some 

 points of detail which require elucidation and as to which 

 discussion may be profitable. It may reasonably be asked : 



(1) If the specialized forms of insect larva have been derived 

 often through degenerative changes from a primitive type 



which differed but little from the adult into which it grew, 

 what clear indications have we as to the nature of this type ? 



(2) If the Endopterygote orders are more highly specialized 

 than the Exopterygota, so that the former may be presumed 

 to have arisen from the latter in the course of the evolution 

 of insect races, how can we imagine the transition from the 

 open to the hidden type of wing-growth to have been brought 

 about ? (3) How far do the facts known as to the past 

 history of insects, through a comparative study of the structure 

 of living adult insects and of extinct groups as shown by 

 fossils preserved in the stratified rocks of the earth's crust, 

 support the views on the history of the class of insects which 

 we infer from a study of the life-histories of families now 

 living on the earth's surface ? 



THE PRIMITIVE TYPE OF INSECT LARVA 



From a comparison of the various larval types presented 

 by the Coleoptera, it has been concluded that the well-armoured, 

 active larva, such as characterizes the carnivorous beetles, 

 the rove-beetles and the dascillids is more primitive than the 

 soft-cuticled grubs of the longhorns or the weevils, with their 

 reduced or vanished legs. This conclusion, though generally 

 admitted by students, has not obtained universal assent. The 

 crawling caterpillar type, recalling the form of a worm or a 

 centipede, has suggested itself to some investigators as indi- 

 cating the nature of the original insect larva, this view has 

 been revived and ably supported 1 in recent times on the 



1 A. Lameere : "La Raison d'etre des Metamorphores chez les Insectes ". 

 Ann. Soc. Entom. Bruxelles, XLIII. 1899. 



