172 ENTOMOLOGY 
These structures are found also in pupe, as those of Sesiidee, 
that force their way out of the stems of plants in which the 
larvee have lived. The emergence from the cocoon is accom- 
plished in some cases by the pupa, in others by the imago. 
Hemerobud, Trichoptera and the primitive lepidopteron 
Eriocephala use the pupal mandibles to cut an opening in the 
cocoon; while many lepidopterous pupz have on the head a 
beak for piercing the cocoon, or teeth for rending or cutting 
the silk. 
Kclosion.—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 (PI. 
2, 4d). 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—F£) with moist body, elongated abdomen and 
miniature wings. Hanging to the empty pupa case (/’), 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 (J ):, 
LT. polyphemus is “* provided with two glands opening into 
the mouth, which secrete during the last few days of the pupa 
state, a fluid which ts 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 
