succession of generations.

The common

trouts of this lake have stomachs like other trouts, which never as far as my experience has gone contain shell fish; but of the gillaroo trout, I have caught with a fly some not longer than my finger, which have had as perfect a hard stomach as the larger ones, with the coats as thick in proportion, and the same shells within; so that this animal is at least now a distinct species, and is a sort of link between the trout and char, which has a stomach of the same kind with the gillaroo, but not quite so thick, and which feeds at the bottom in the same way. I have often looked in the lakes abroad for gillaroo trout, and never found one. In a large lake at the foot of the Crest of the Brenner— above 4,000 feet above the level of the sea, I once caught some trout, which, from their thickness and red spots, I suspected were gillaroo, but on opening the stomach I found I was mistaken, it had no particular thickness, and was filled with grasshoppers; but there were char, which fed on shell fish, in the same lake.

POIET. Are water flies found

rivers?

on all

HAL.-This is a question which I find it impossible to answer; yet from my own experience I should suppose, that in all the habitable parts of the Globe certain water flies exist wherever there is running water. Even in the most ardent temperature, gnats and musquitoes are found, which lay their congeries of eggs on the water, which, when hatched, become first worms, afterwards small shrimp-like aurelia, and lastly flies. There are a great number of the largest species of these flies on stagnant waters and lakes, which form a part of the food of various fishes, principally of the carp kind: but the true fisherman's flies,-those which are imitated in our art, principally belong to the northern, or at least temperate part of Europe, and I believe are nowhere more abundant than in England. It appears

to me, that since I have been a fisherman, which is now the best part of half a century, I have observed in some rivers where I have been accustomed to fish habitually, a dimi

nution of the quantity of fly. There were always some seasons in which the temperature was favourable to a quantity of fly; for instance, fine warm days in spring for the grannam, or brown fly; and like days in May and June for the alder fly, May fly, and stone fly; but I should say that within these last twenty years I have observed a general diminution of the spring and autumnal flies, except in those rivers which are fed from sources that run from chalk, and which are almost perennial-such as the Wandle, and the Hampshire and Buckinghamshire rivers; in these streams the temperature is more uniform, and the quantity of water does not vary much. I attribute the change of the quantity of flies in the rivers to the cultivation of the country. Most of the bogs or marshes which fed many considerable streams are drained; and the consequence is that they are more likely to be affected by severe droughts and great floods -the first killing, and the second washing away the larvæ and aurelias. May flies thirty years ago were abundant in the upper

part of the Teme river in Herefordshire, where it receives the Clun: they are now seldom or rarely seen. And most of the rivers of that part of England, as well as of the west, with the exception of those that rise in the still uncultivated parts of Dartmoor and Exmoor, are after rain rapid and unfordable torrents, and in dry summers little more than scanty rills. And Exmoor and Dartmoor, almost the only great remains of those moist, spongy or peaty soils which once covered the greatest part of the high lands of England, are becoming cultivated, and their sources will gradually gain the same character as those of our midland and

highly improved counties. I cannot give you an idea of the effects of peat mosses and grassy marshes on the water thrown down from the atmosphere, better, than by comparing their effects to those of roofs of houses of thatched straw, as contrasted with roofs of slate, on a shower of rain. The slate begins to drop immediately, and sends down what it receives in a rapid torrent, and is dry soon after the shower is over. The roof of

thatch, on the contrary, sponge like, is long before the water drops from it; but it continues dropping and wet for hours after the shower is over and the slate is dry.

POIET.-You spoke just now of the gillaroo trout, as belonging only to Ireland. I

can, however, hardly bring myself to believe that such a fish must not be found elsewhere. For lakes with shell fish and char are common in various parts of Europe, and as the gillaroo trout is congenerous, it ought to be found both in Scotland and the Alpine countries.

F