VARIETIES OF TROUT. 279 



All Trout are very variable. The characters which Dr." Giinther considered 

 of most importance in defining species of Trout were the number of vertebrae, 

 and the number of pyloric appendages to the intestine. On evidence of this 

 kind he separated northern and southern forms of Salmo fario, because the 

 southern fish had fewer vertebrae ; but Mr. Day has met with individuals 

 having the larger number of vertebrae as far south as Cardiganshire, while Dr. 

 Cobbold found only fifty-six vertebra? in a Salmo fario in Scotland. Salmo 

 fario has vertebra? numbering from fifty-six to sixty, and all the other 

 British fresh-water Trout which do not migrate have a number of vertebrae 

 which is between these limits. The variation of the pyloric caecal appendages 

 in this species in Britain ranges between thirty-three and forty-seven. 



The common Brook Trout was taken from the Itchen, near Winchester, and 

 from the Thames, to Tasmania, and thence to New Zealand. Under the 

 different conditions of food, these Trout in Otago became fat and plump almost 

 to deformity. Instead of increasing, as in Scotland, about one-third of a 

 pound a year, they increase from one to two and three-quarter pounds a year, 

 and reach a weight of twenty-one pounds or more. They vary, too, in propor- 

 tions and colour, while the caecal appendages vary from thirty-three to sixty- 

 one in the female, and from thirty-seven to fifty-five in the males examined. 

 In all British Trout, excepting the Loch Leven Trout, the variation in. number 

 of these appendages ranges between thirty-three and fifty, so that we are 

 compelled to conclude that the number of these appendages is dependent on 

 food, and valuable as a specific character only in so far as species depend upon 

 the conditions of existence. Even the colour of the flesh is variable. 



Mr. Day mentions that in the lower part of the Itchen beyond Alresford 

 crustaceans abound, while they do not occur in the upper part of the stream ; 

 and that the flesh of the cooked Trout from the lower part of the river cuts 

 pink, while in the upper part of the Itchen it is nearly white. This author, in 

 evidence that the colour of the flesh varies with the food, mentions that where 

 the American Charr, Salmo fontinalis, has been turned out into the rivers of 

 Cardiganshire they are good and rich, with a peculiar gamboge colour. The 

 same species in Perthshire is fat, with the firm flesh of a beautiful pearly white, 

 while in other localities it is said to be pink. Hence we can only conclude 

 that the colour of the flesh may vary ; the same species of Trout is known 

 similarly to vary in contiguous streams in Wales. 



The external colours change with the nature of the soil or bottom of 

 the water, the character of the current, the extent and depth of the water, 

 as well as with temperature, light, and food. Mr. Day tells us that clear 

 water in rapid rivers or lakes with a pebbly bottom frequently produces 

 silvery fish with X-shaped black marks. The colour is imitative, and the fish 



