140 ENTOMOLOGY 



through the line texture of the wall; then a gummy resinous substance, 

 sometimes of a light brown color, is spread over all the inside of the cocoon. 

 The larva continues to work for four or five days, hardly taking a few 

 minutes of rest, and finally another coating is spun in the interior, when 

 the cocoon is all finished and completely air tight. The fibre diminishes 

 in thickness as the completion of the cocoon advances, so that the last 

 internal coating is not half so thick and so strong as the outside ones." 

 (Trouvelot.) 



Emergence of Pupa. Subterranean pupae wriggle their way to the 

 surface of the ground, often by the aid of spines (Fig. 217), that catch 

 successively into the surrounding soil. These locomotor spines may occur 

 on almost any part of the pupa, but occur commonly on the abdominal 

 segments, as in lepidopterous pupae; the extremity of the abdomen, also, 

 bears frequently one or more spinous projections, as in Tipulidas, Cara- 



bidae and Lepidoptera, to assist the escape of the pupa. 

 These structures are found also in pupae, as those of 

 Sesiidae, that force their way out of the stems of plants 

 in which the larvae have lived. The emergence from 

 the cocoon is accomplished in some cases by the pupa, 

 in others by the imago. Hemerobiidas, Trichoptera 

 and the primitive lepidopteron Eriocephala use the 

 pupal mandibles to cut an opening in the cocoon; 

 while many lepidopterous pupae have on the head a 

 beak for piercing the cocoon, or teeth for rending or 

 FIG. 2i 7 .-Sub- cutting the silk. 



terranean pupa of 



Anisota. Enlarged. Eclosion. During the last few hours before the 



emergence of a butterfly the colors of the imago develop 

 and may be seen through the transparent skin of the chrysalis (PL II A}. 

 No movement occurs, however, until several seconds before emergence; 

 then, after a few convulsive movements of the legs and thorax of the 

 imprisoned insect, the pupa skin breaks in the region of the tongue and 

 legs (B), a secondary split often occurs at the back of the thorax, and 

 the butterfly emerges (C-E) with moist body, elongated abdomen and 

 miniature wings. Hanging to the empty pupa case (F), or to some other 

 available support, the insect dries and its wings gradually expand (G, H) 

 through the pressure of the blood. At regular intervals the abdomen 

 contracts and the wings fan the air, and sooner or later a drop or two of 

 a dull greenish fluid (the meconium) is emitted from the alimentary canal. 

 The expansion of the wings takes place rapidly, and in less than an hour, 

 as a rule, they have attained their full size (/). 



