no The Under-Water World 



snare, the larva waits until some small 

 creature becomes entangled in the mesh, 

 whereupon it dashes forth and seizes it, 

 lor the snare-building species are car- 

 nivorous, not herbivorous like the great 

 majority of the caddis- worms. When 

 the time for pupation arrives the end of 

 the case is sealed and the change takes 

 place within. In due time the perfect 

 insect is ready for emergence and the 

 pupa, forcing its way through the sealed 

 entrance of the case, rises to the surface 

 of the water. In some species the pupa 

 manages to propel its way to some 

 floating leaf or other support before the 

 skin splits and the imago frees itself ; 

 but in other species the emergence is 

 effected direct from the surface of 

 the water. Along each side of the 

 larva's abdomen are a series of filamen- 

 tous processes acting as tracheal gills, 

 absorbing the oxygen in the water. By 

 an undulating movement of the body 



