INSECT METAMORPHOSIS 



have rudimentary or shortened wings in the adult stage 

 often have wings larger than those of the adult, indicat- 

 ing that the wings have been reduced in the adult since 

 the time when the pupa was first established. Here, 

 therefore, we see a case of metamorphosis between the 

 pupa and the adult. Adult moths and butterflies have no 

 mandibles or have mere rudiments of them (Fig. 163), 

 but the jaws are often quite visible in the pupae (Fig. 

 159 H, Md), and the pupa of one moth has long, toothed 

 mandibles which it uses to liberate itself from the cocoon 

 before transforming to the adult. 



The structural changes that accompany the transfor- 

 mation of the larva into an adult insect are by no means 

 confined to the outside of the body. Much internal re- 

 organization goes on which involves changes in the tissues 

 themselves. The larva may have built up a highly effi- 

 cient alimentary canal well adapted for handling its own 

 particular kind of food, but perhaps the adult has adopted 

 an entirely different diet. The alimentary canal, there- 

 fore, must be completely remodeled during the pupal 

 stage. The nervous system and the tracheal system are 

 often different in the larval and the adult stages, but the 

 change in these organs is usually in the nature of a greater 

 elaboration for the purposes of the adult, though the 

 larva may have developed special features that are dis- 

 carded. 



It is in the muscles usually that the most radical re- 

 constructive processes of the transformation from larva to 

 adult take place. The muscles of adult insects are at- 

 tached to the outer cuticular layer of the body wall, which 

 in hard-bodied insects constitutes the "skeleton," and the 

 mechanical differences between the larva and the adult 

 lie in the relation between the muscles and the cuticula. 

 With the change in the external parts between the two 

 active stages of the insect, therefore, the larval muscles 

 are likely to become entirely unsuited to the purposes of 

 the adult. The special larval muscles, then, must be 



I *55 ] 



