164 ENTOMOLOGY 



involving the cruciform condition, Packard finds in the neu- 

 ropterous genus Mantispa (Fig. 211), the first larva of which 

 is truly campodea-form and active. Beginning a sedentary 

 life, however, in the egg-sac of a spider, it loses the use of its 

 legs and the antennae become partly aborted, before the first 

 moult. In Packard's words, " Owing to this change of hab- 

 its and surroundings from those of its active ancestors, it 

 changes its form, and the fully grown larva becomes cylin- 

 drical, with small slender legs, and, owing to the partial disuse 

 of its jaws, acquires a small, round head." Meloidae (Fig. 

 217) afford other excellent examples of the transition from 

 the thysanuriform to the cruciform condition during the life 

 of the individual. 



Thysanuriform characters become gradually suppressed in 

 favor of the cruciform, until, in most of the highly developed 

 orders (Mecoptera, Trichoptera, Lepidoptera, Diptera, Si- 

 phonaptera and Hymenoptera) , they cease to appear, except 

 for a few embryonic traces an illustration of the principle of 

 " acceleration in development." 



Growth. The larval period is pre-eminently one of growth. 

 In Heterometabola, growth is continuous during the nymphal 

 stage, but in Holometabola this important function becomes 

 relegated to the larval stage, and pupal development takes 

 place at the expense of a reserve supply of food accumulated 

 by the larva. 



The rapidity of larval growth is remarkable. Trouvelot 

 found that the caterpillar of Telea polyphemus attains in 56 

 days 4,140 times its original weight (1/20 grain), and has 

 eaten an amount of food 86,000 times its primitive weight. 

 Other larvae exceed even these figures; thus the maggot of a 

 common flesh fly attains 200 times its original weight in 24 

 hours. 



Ecdysis. The exoskeleton, unfitted for accommodating 

 itself to the growth of the insect, is periodically shed, and 

 along with it go not only such integumentary structures as 

 hairs and scales, but also the chitinous lining, or intima, of 



