CAbDIS-FLIES. 97 



the case and for the exit of excreta. One larva 

 had chosen a piece of a hollow rectangular stem 

 about f inch long, and had covered the ends with 

 a membrane-like material, with a few pieces of 

 stem and other material woven in, and at the pos- 

 terior end was the little circular hole before men- 

 tioned. 



The larvae seemed to feed on microscopic growths 

 on the stems and leaves of the water plants, for they 

 continually passed along the water weeds not gnaw- 

 ing off pieces, but just bruising the delicate leaves 

 of the plant, for with the lens one could see little 

 bruised places on the leaves, while the stems were 

 unafiFected. 



The legs and the way the larvae use them are 

 rather interesting. The three pairs are all of 



different sizes. The hind pair is very long and 

 when floating on its back near the surface of the 

 Avater as the larvae frequently did, these legs were 

 gently moved like oars. Also in climbing upwards 

 along a stem, they were first placed forward to 

 get a reach, and then the smaller pairs were brought 

 into play, and the body pulled forward. The front 

 pair is the shortest, and as the creature moves 

 quickly forward one can see how the marked differ- 

 ence in length is rather a help than hindrance, 

 for the hind pair takes a good long reach, the next 

 pair a lesser reach, and the front pair just an ordin- 

 ary step. One could observe this well, for these 

 larvae had a habit of moving along on their backs, 

 both in swimmir.g and in walking along plants, 

 but they could quickly turn themselves round 

 again. They rested frequently from the labour 



