218 STATES OF INSECTS. (Larva.) 
Withdrawing her head, she extends silken longitudinal 
threads between the two margins, and thus unites them. 
This part is more clumsy, and not so regular as the rest 
of the cocoon, so that the point of union is always dis- 
coverable. These caterpillars do not always divide the 
cocoon into two egual portions, for often they will finish 
three quarters of a cocoon before they enter it, and be- 
gin at the other end*. 
The general rule is,—that each larva spins for itself a 
separate cocoon; but amongst those of Arctia chry- 
sorheea and others which live in society, two or three 
sometimes begin their operations’ so close together that 
they are under the necessity of forming one common co- 
coon, which serves for a covering to the whole number. 
The same thing happens to silk-worms, the double 
or treble cocoons of which are called Dupions by the 
breeders. The larve of some Ichneumons, besides 
forming each its separate cocoon, spin a joint cottony 
covering for the whole”, which is effected thus :—After 
they leave the caterpillar they have devoured, they fix 
themselves side by side at a little distance from it, and 
begin to spin each a cocoon; and in order to defend its 
end and side that is not covered by others, they spin 
further an envelope of loose silk, and thus this exterior 
covering is formed. 
The size, figure, colour, substance, and texture of 
silken cocoons are extremely various. Their size indeed 
is usually proportioned to that of the included larva or 
pupa; yet it is by no means always so. Some large ca- 
terpillars spin cocoons so small, that the observer can 
’ @ De Geer i. 463—. 
» Reaum. it, Mem. xi. Comp. De Geer ii. 162. Reaum. ii.424. 
