Aquatic Insects 109 



which is more or less closed, the front 

 end being left open to allow the larva 

 to protrude its head and legs. Hooks 

 are present on the end of the abdomen, 

 enabling the larva to anchor itself safely 

 in its case. The abdomen is very soft, 

 but the head and thoracic segments 

 have a harder covering, better able to 

 resist attack. As the larva grows and 

 so becomes too large for its home it adds 

 to the front end of its case, and cuts 

 off a piece at the back ; in fact, it 

 makes its home grow with it a very 

 accommodating proceeding. Some of the 

 leaf-built cases are very difficult to detect 

 when the owners are crawling among the 

 water-weeds. There are a few species 

 that do not construct these travelling 

 houses, but in their stead spin a silken 

 web among the weeds somewhat resem- 

 bling that of certain spiders. Lurking 

 within this contrivance, which serves 

 both as a means of protection and a 



