I/ 2 ENTOMOLOGY 



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 accom- 

 plished in some cases by the pupa, in others by the imago. 

 Hemerobiidae, 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 cutting 

 the silk. 



Eclosion. During the last few hours before the emer- 

 gence of a butterfly the colors of the imago develop and may 

 be seen through the transparent skin of the chrysalis (PL 

 2, 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 (5), 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 (/). 



T. polyphennts is " provided with two glands opening into 

 the mouth, which secrete during the last few days of the pupa 

 state, a fluid which is a dissolvent for the gum so firmly unit- 

 ing the fibres of the cocoon. This liquid is composed in great 

 part of bombycic acid. When the insect has accomplished the 

 work of transformation which is going on under the pupa 

 skin, it manifests a great activity, and soon the chrysalis cover- 

 ing bursts open longitudinally upon the thorax ; the head and 

 legs are soon disengaged, and the acid fluid flows from its 



