LEPIDOPTERA. . 155 
head to pass gently over the last quarter of the circle. At last 
the caterpillar finds itself bound on the second side; the head 
rests on the thread-covered plane, and the insect fixes the second 
end of the thread.” 
It has only to repeat the same manceuvre as many times as 
there are threads wanted to make a strong band. But each 
thread embraces the head, 
or rather the lower part 
of the head, for it knows 
how to make each thread 
it spins glide into the 
bend or crease of its 
neck by a little movement of its head. It must disengage its 
head from under the band, not a difficult opera- 
tion. It causes it to slide along the threads near 
one of the places where they are fixed, and it is 
then in the position indicated by the foregoing 
engraving (Fig. 109). 
About thirty hours after the caterpillars have 
succeeded in making themselves fast, they have 
completed their transformation into chrysalides, 
Fig. 110, where the chrysalis of the above- 
mentioned caterpillar is seen in two different 
positions, and held by the same band which first 
supported the caterpillar. 
Those caterpillars which construct cocoons, make 
them of silk and other substances. These cocoons 
are, for the most part, oval or elliptical, some- 
times boat-shaped, and ordinarily white, yellow, 
or brown in colour. The threads may very slightly 
adhere together, or be closely united by a gummy 
substance with which the caterpillar lines the in- ed OM Daa oF 
terior of the cocoon, and which it expels from the — Pits bmssice. 
anus. Some cocoons are composed of a double envelope, others are 
of an uniform texture. Some are of a tissue so close that they 
entirely hide the chrysalis contained within; others form a very 
light covering, through which the chrysalis can be easily perceived 
(Fig. 111). 

Fig. 109.—Caterpillar of the Pieris brassice. 

