DEVELOPMENT i 7a 
of silk around a twig, then a fibre is attached to a leaf near 
by, and by many times doubling this fibre and making it 
shorter every time, the leaf is made to approach the twig at 
the distance necessary to build the cocoon; two or three leaves 
are disposed like this one, and then fibres are spread between 
them in all directions, and soon the ovoid form of the cocoon 
distinctly appears. This seems to be the most difficult feat 
for thé worm to accomplish, as after this the work is simply 
mechanical, the cocoon being made of regular layers of silk 
united by a gummy substance. The silk is distributed in zig- 
zag lines of about one-eighth of an inch long. When the 
cocoon is made, the worm will have moved his head to and 
fro, in order to distribute the silk, about two hundred and 
fifty-four thousand times. After about half a day’s work, the 
cocoon is so far completed that the worm can hardly be dis- 
tinguished through the fine texture of the wall; then a gummy 
resinous substance, sometimes of a light brown color, 1s spread 
over all the inside of the cocoon. ‘The larva continues to work 
for four or five days, hardly taking a 
Fic. 216. 
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 thick- 
ness as the completion of the cocoon 
advances, so that the last internal coat- 
ing is not half so thick and so strong 
as the outside ones.”’ (Trouvelot.) 
Emergence of Pupa.—Subterranean 
pup wriggle their way to the surface Subterranean pupa of 
Anisota. Enlarged. 
of the ground, often by the aid of spines 
(Fig. 216) 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 pupz ; the extremity of the abdomen, also, bears 
frequently one or more spinous projections, as in Tipulide, 
Carabide and Lepidoptera, to assist the escape of the pupa. 
