V CADDIS-WORMS 243 



grandfathers. But with these aquatic larvae it is not 

 a question of caprice or fashion ; their dress is care- 

 fully adapted to the actual needs of life. They 

 employ very different materials, and the kind of 

 material largely affects the dress which they put on. 

 They make use of whole or nearly whole leaves, 

 bits of leaves, and these of a great number of species, 

 or little sticks and straws. Others use seeds, 

 roots, grains of sand and gravel, or the shells of 

 water-snails and bivalves ; in short, all the materials 

 which can be found in water are employed by par- 

 ticular Caddis-worms. In some sheaths one only of 

 these materials is employed, and these are the most 

 neatly constructed. In other sheaths a number of 

 different materials are made use of, so that the larva 

 is dressed, so to speak, in rags and tatters, and its 

 covering is altogether shapeless. 



" Every sheath is a hollow cylinder with an open- 

 ing at each end. The fore end, out of which the 

 head and the six limbs can be passed, is wide. 

 The hinder end is narrow, and closed by a circular 

 silken plate with a hole in it. [The hinder end 

 is often quite open. Some species make cases of 

 uniform width.] 



" If the sheath is made of leaves, it may take a 

 flattish form, wide in proportion to its depth, but 

 there are few of this kind. [Limnophilus pellucidus.] 

 In general the shape is cylindrical. Some sheaths 

 are covered externally by bits of rushes or small 

 twigs glued together and arranged lengthwise. Some- 

 times the rushes are so artfully joined that they look 

 like a grooved cylinder without joints, but it is rare to 



