MAY-FLIES AND THEIR NEIGHBOURS 225 



by the larva ; the second is composed of com- 

 paratively large pieces of sandstone ; the next in 

 order is a neat form made of minute pieces of 

 wood cut into nearly equal lengths ; four and five 

 are the homes of species which often build their 

 cases of rushes combined with various shells of 

 water molluscs. These latter are used with or 

 without the consent of their tenants, who, when 

 once attached by the insoluble cement of the 

 caddis-worm, become close prisoners and are 

 dragged hither and thither entirely at the mercy 

 of the grub. Number six represents another case 

 built of stone, with one large stone attached at 

 the side to make up for a general deficiency in 

 weight. This kind of weighting is frequently 

 done when the case happens to have been made 

 too light in the first instance. Number seven is 

 formed of convenient lengths of rushes ; eight is 

 composed of everything as yet mentioned, in- 

 cluding shells, stones, wood, rushes, &c. In nine 

 and ten, however, we get a new variety, for these 

 are thin tubes built of tiny grains of sand closely 

 cemented together, to the outside of which are 

 long twigs fixed, like the heavy stone of the former 

 instance, for the purpose of giving a balance. 

 The bottom row shows some of these forms as 

 they appear end on. 



These aquatic architects arrange and build 



