1 68 



ENTOMOLOGY 



FIG. 212. 



Obtect pupa of milk- 

 weed butterfly, Anosia 

 plexippus, natural size. 



and body are compactly united ; as distinguished from the free 

 pupa of Neuroptera, Trichoptera, Coleoptera and others, in 

 which the appendages are free (Fig. 203). This distinction, 

 however, cannot always be drawn sharply. Diptera present 

 also the coarctate type of pupa (Fig. 

 204), in which the pupa remains en- 

 closed in the old larval skin, or pupa- 

 rium. 



Pupal characters, though doubtless of 

 great adaptive and phylogenetic signifi- 

 cance, have received but little attention. 

 Lepidopterous pupae present many puz- 

 zling characters, for example, an eye- 

 like structure (Fig. 213) suggesting 

 an ancestral active condition, such as 

 still occurs among heterometabolous in- 

 sects. 



Pupation of a Caterpillar. The process of pupation in 

 a caterpillar has been carefully observed by Riley. The cater- 

 pillar of the milkweed butterfly (PL I, A) spins a mass of 

 silk in which it entangles its suranal plate and anal prolegs 

 and then hangs downward, bending up 

 the anterior part of the body (5), 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 con- 

 tortions of the larva. 



The way in which the pupa becomes at- 

 tached to its silken support is rather com- 

 plex. Briefly, while the larval skin still 

 retains its hold on the support, the posterior end of the pupa 

 is withdrawn from the old integument and by the vigorous 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 (E) and soft, but in an hour or so 



FIG. 213. 



Head of chrysalis of 

 Papilio polyxenes, to 

 show eye-like structure. 

 Enlarged. 



