50 SALMON I A. [second day 



"Wales, is three or four times as large, and has brown 

 wings, which likewise protrude from the back, and its 

 wings are shaded like those of a partridge, brown and 

 yellow brown. These three kinds of flies lay their 

 eggs in the water, which produce larva? that remain 

 in the state of worms, feeding and breathing in the 

 water till they are prepared for their metamorphosis 

 and quit the bottoms of the rivers, and the mud and 

 stones, for the surface, and the light and air. The 

 brown fly usually disappears before the end of April, 

 likewise the grannam ; but of the blue dun there is 

 a succession of different tints, or species, or varieties, 

 which appear in the middle of the day all the summer 

 and autumn long. These are the principal flies on 

 the Wandle — the best and clearest stream near 

 London. In early spring these flies have dark olive 

 bodies; in the end of April and the beginning of 

 May, they are found yellow ; and in the summer, they 

 become cinnamon-coloured ; and again, as the winter 

 approaches, gain a darker hue. I do not, however, 

 mean to say that they are the same flies ; but more 

 probably successive generations of Ephemerae of the 

 same species. The excess of heat seems equally 

 unfavourable, as the excess of cold, to the existence 

 of the smaller species of water-insects, which, during 

 the intensity of sunshine, seldom appear in summer, 

 but rise morning and evening only. The blue dun 



