FLIES. 53 



production, they become less fat, particularly 

 the females ; the large quantity of eggs and 

 their size probably affecting the health of 

 the animal, and compressing generally the 

 vital organs in the abdomen. They are at 

 least six weeks or two months after they 

 have spawned before they recover their 

 flesh: and the time when these fish are at 

 the worst, is likewise the worst time for fly 

 fishing, both on account of the cold weather 

 and because there are fewer flies on the 

 water than at any other season. Even in 

 December and January there are a few 

 small gnats or water flies on the water in 

 the middle of the day, in bright days, or 

 when there is sunshine. These are gene- 

 rally black, and they escape the influence of 

 the frost by the effects of light on their 

 black bodies, and probably by the extreme 

 rapidity of the motions of their fluids, and 

 generally of their organs. They are found 

 only at the surface of the water, where the 

 temperature must be above the freezing 

 point. In February a few double winged 

 water flies which swim down the stream are 



