190 INSECT ARTIZANS AND THEIR WORK 



make an entirely new dwelling. It fastens its old 

 case to the basal portion of a leaf close to the edge, 

 and then mines out a space along the margin of the 

 leaf, nearly twice the length and double the width 

 of its body. To do this it comes, of course, quite 

 outside its old case, and when the space is quite 

 completed it severs the large new case from the 

 leaf in the same manner as it did when making 

 its first case, and then crawls off to feed. This 

 new case is rather flimsy and translucent, but in a 

 day or two the larva causes it to become very tough 

 and quite opaque. 



" The inside of all the Coleophorid cases I have 

 examined is lined with silk. The threads, running 

 in all directions, are plainly visible under the 

 microscope. It is this silk lining which, by pro- 

 viding a firm foothold for the larva, enables it 

 almost instantaneously to withdraw its body into 

 the case when alarmed. I think it highly probable 

 that the interior of the case is also strengthened by 

 some other material secreted by the larva, as many 

 cases appear to be formed of a substance resembling 

 parchment which could hardly be formed by leaf- 

 cuticle and silk threads without the aid of some 

 stiffening material. Dr. Wood suggests that this 

 material may be the product of the salivary glands." 



The new case, as Sich goes on to tell us, is straight, 

 cylindrical, and has about thirty times the capacity 

 of that in which it passed the winter. It feeds 

 for about a fortnight longer on the lower side of 

 the leaf, then removes to the upper side, fastens its 



