10 



that A'arles more in appearance and quality. From the varieties 

 of color — deviations in the spots — and external differences of 

 shape, a plurality of species has been frequently inferred. But it 

 seems now to be well ascertained that wo have only one single 

 species in our rivers ; and my own experience certainly confirms 

 it. No matter how nature may clothe the skeleton of certain 

 specimens, so long as the osteology remains unchanged, the species 

 is unchanged. The apparent varieties are easily accounted for. 

 The different strata through which the rivers flow, must impreg- 

 nate the water with their peculiar chemical properties, and thus 

 affect both the appearance and the quality of their inhabitants. 

 I have witnessed this in some trout, taken from holes whence 

 peat had been extracted, and which had become filled with water. 

 These fish were not only dark, but very dark — scarcely a lighter 

 color than the peat itself; while in the neighbouring river, from 

 which they had, no doubt, been driven by floods, they were peculiarly 

 bright and beautiful. The variety and quality of their food, will 

 also make a difference. Yet neither the food nor the water are 

 to be exclusively charged with this ; for the brightest fish, in the 

 clearest stream, if he take up his abode under a low bridge, or in 

 a thickly sheltered situation, becomes much darker than his 

 brethren, who sport in more exposed positions. Hence it appears 

 that light is essential to the brilliancy of fish, as well as of plants : 

 and so is good condition ; for we never see a bright colored fish 

 immediately after spawning — the only season when they become 

 thin and poor. Circumstances, therefore, determine these varia- 

 tions, and not distinction of species. Even the gilleroo trout of 

 Ireland, whose stomach is unlike that of any other of the salmonidaa 

 (being thickened into a substance resembling the gizzard of a 

 fowl), has still the fifty-six vertebrae of the common trout, and is 

 clearly nothing else. It has been imagined, and with great 

 probability, that the thickening and hardening of the stomach is 

 an accommodation of nature to the peculiarity of the food; which 

 is found to be, almost exclusively, small crustaceous animals : 

 and we are too well satisfied of the adaptability of the animal 

 frame to circumstances, to consider this as any thing very 

 remark? blp. 



