12 INSECT ARTIZANS AND THEIR WORK 



fragments of rasped bark and cements the whole 

 with a plentiful supply of liquid silk which sets 

 very hard. If one of these caterpillars is put into 

 a glass vessel, so that there is nothing it can gnaw 

 for this purpose, the resulting cocoon will be 

 transparent and glass-like. 



A section cut from one of these cocoons is not 

 to be distinguished — even with the aid of a pocket 

 lens — from actual bark. It may therefore be ques- 

 tioned whether it should be included among 

 spinners and weavers ; but the first stage at least is 

 pure spinning, and the finished article shows how 

 the product of the silk-glands may be utilized to 

 elaborate a structure wholly different from the 

 ordinary web-cocoon. The head end of the cocoon 

 is said to be made of thinner material than the 

 rest, the object being to offer less resistance to the 

 emergence of the moth. 



But this is not invariably the case. At the time 

 of writing these lines we have opened a Puss cocoon 

 from which no moth had emerged, and found the 

 upper end of the cocoon actually much thicker 

 than the other parts. The moth had succeeded in 

 throwing off the chrysalis skin, but had evidently 

 been unprovided with the dissolvent fluid, for there 

 was no sign of its action on the glazed lining of the 

 cell. So the insect had perished. To the same 

 end the front part of the chrysalis skin has a low 

 sharp ridge with which it cracks the cocoon, and 

 this part of the skin remains attached to the moth's 

 head until after emergence. The reason for this 



