. c- 



K,,f 



DEVELOPMENT 



147 



I 



Coleoptera and others, in which the appendages are free (Fig. 206); 

 but this distinction cannot always be drawn sharply. Diptera present 

 also the coarctate type of pupa (Fig. 207), in which the pupa remains 

 enclosed in the old larval skin, or puparium. 



Pupal characters, though doubtless of great adaptive and phylogene- 

 tic significance, have received but little attention. Lepidopterous pupae 

 present many puzzling characters, for example, an eye-like structure 

 (Fig. 216) suggesting an ancestral active condition, such as still occurs 

 among heterometabolous insects. 



FIG. 215. Obtect 

 pupa of milkweed but- 

 terfly, Anosia plexip- 

 pus, natural size. 



FIG. 216. Head 

 of chrysalis of Pa- 

 pilio polyxenes, to 

 show eye-like struc- 

 ture. Enlarged. 



Pupation of a Caterpillar. The process of pupation in a caterpillar 

 has been carefully observed by Riley. The caterpillar of the milkweed 

 butterfly (PI. I, A) spins a mass of silk in which it entangles its suranal 

 plate and anal prolegs and then hangs downward, bending up the ante- 

 rior part of the body (B) , which gradually becomes swollen. The skin of 

 the caterpillar splits dorsally from the head backward, and is worked 

 back toward the tail (C and D) by the contortions of the larva. 



The way in which the pupa becomes attached to its silken support 

 is rather complex. Briefly, while the larval skin still retains its hold on 

 the support, the posterior end of the pupa is withdrawn from the old 

 integument while the latter is being temporarily gripped between two 

 of the abdominal segments of the pupa, and by the vigorous whirling 

 and twisting of the body the hooks of the terminal cremaster of the pupa 

 are entangled in the silken support. At first the pupa is elongate () 

 and soft, but in an hour or so it has contracted, hardened, and assumed 

 its characteristic form and coloration (F) . 



Pupal Respiration. Except under special conditions, pupae breathe 

 by means of ordinary abdominal spiracles. Aquatic pupae have special 



