silk. Silk is a viscouy fluid secreted by elongated ^acs located in the dorsal region. 

 These sacs communicate with a minute tube-like organ, known as the spinneret, 

 which is located on the under side of the head of the caterpillar, just back of the 

 mandibles. The fluid silk, as it is ejected through the spinneret, immediately 

 hardens on contact with the air and is deposited in the form of very fine threads or 

 filaments which the caterpillar uses for various purposes, sometimes as lines with 

 which to guide itself from place to place and enable it to retrace its steps to its 

 favorite resting-place, sometimes to tie together the leaves in which it forms its nest, 

 or to weave a sort of shelter in which it conceals itself, and finally to make the little 

 buttons and the girdles by which, as we shall see later, the chrysalis is held in 

 place. Many moths weave from silk compact structures known as cocoons, in 

 which the chrysalis is lodged. Butterflies do not weave true cocoons. 



The time spent by the insect in the egg is generally short. The time passed in 

 the larval state may be short or long. When butterflies hibernate, or pass the 

 winter, as caterpillars, the time spent in this state is long, and especially in the case 

 of those species which inhabit arctic regions. There are some butterflies which 

 occur north of the Arctic Circle, and we have ascertained that these, because the 

 summers are so short in the far north, pass two summers and the intervening winter 

 in the larval condition, and another winter in the pupal stage, before they emerge 

 and take wing. On the other hand, under more temperate conditions butterflies of 



