162 



ENTOMOLOGY 



stalk (Fig. 223), and the processes of histolysis and histogenesis become 

 extremely complicated. The hypodermis, muscles, alimentary canal 

 and fat-body are gradually broken down and remodeled, and part of 

 the respiratory system is reorganized, though the dorsal vessel and the 



central nervous system, uninterrupted in 

 their functions, undergo comparatively 

 little alteration. 



The imaginal hypodermis of the tho- 

 rax arises from thickenings of the peri- 

 podal membrane which spread over the 

 larval hypodermis, while the latter is 

 gradually being broken down by the 

 leucocytes; in the head and abdomen 

 the process is essentially the same as in 

 the thorax, the new hypodermis arising 

 from imaginal buds. 



Most of the larval muscles, excepting 

 the three pairs of respiratory muscles, 

 undergo dissolution. The imaginal 

 muscles have been traced back to meso- 

 dermal cells such as are always associated 

 with imaginal buds. 



Hymenoptera and Lepidoptera. 

 The internal transformation in Hymen- 

 optera, according to Bugnion, is less pro- 

 found than in Muscidae and more exten- 

 sive than in Coleoptera and Lepidoptera. 

 The internal metamorphosis in Lepidop- 

 tera resembles in many respects that of 

 Corethra. In both these orders the dorsal 

 pair of prothoracic buds is absent. In 



a full-grown caterpillar the fundaments of the imaginal legs and 

 wings (Fig. 224) may be seen, the wings in a frontal section of the 

 larva appearing as in Fig. 225. Many of the details of the internal 

 metamorphosis in Lepidoptera have been described by Newport and 

 Gonin. Figure 226, after Newport, shows some of the more evi- 

 dent internal differences in the larva, pupa and imago of a lepidop- 

 terous insect. 



Significance of Pupal Stage. To repeat among holometabolous 

 insects the function of nutrition becomes relegated to the larval stage 



PIG. 224. Imaginal buds of full 

 grown larva of Pieris, dorsal aspect. 

 b, brain; m, mid intestine; s l , pro- 

 thoracic spiracle; s 4 , first abdominal 

 spiracle; sg, silk gland; I, pro- 

 thoracic bud; II, bud of fore wing; 

 III, bud of hind wing. After 

 GONIN. 



