IN FISH. 93 



temperature. It will thus be seen incidentally that the supply is 

 limited, inasmuch as the proper conditions are not always attain- 

 able. P'or condensing purposes a bountiful supply of water would 

 not be stored at all after once being used, but allowed to run waste. 

 On the other hand, a scant supply would often become hot and 

 dirty by frequent usage, and so become unfit to sustain healthy life. 

 Goldfish are carp, and are found in the same pond in considerable 

 variety of colour, from sooty black to white, with all shades of gold 

 and yellow intervening. They are often coloured in patches of red 

 and black or red and white ; very rarely all three colours are found, 

 but never, so far as I know, are black and white found in the same 

 fish without some admixture of red. The circumstances which gave 

 rise to the present investigation are as follows : Some two or three 

 years ago, a mill-dam in which large numbers of Goldfish w^ere 

 being reared became tenanted by a water weed (Potamogeton) which 

 had been accidentally introduced by the nets of the man who rented 

 the fishing. A short time sufficed to develop the growth of the 

 weed to such an extent that a net could not be used for fishing 

 without first cutting away the weeds by means of ropes or wire ; 

 and further, it was found that in some twelv^e or eighteen months' 

 time the proportion of Golden-coloured fish to that of the dark and 

 black ones was considerably diminishing, and in two years the 

 number was so reduced that it was scarcely worth while to fish the 

 pond at all. To remedy this state of things, and find means to 

 ensure a more certain supply of Gold and Silver-coloured fish, is 

 the object now in view. I trust we shall be able to show how a 

 considerable change may be made in the shade of colour both in 

 red and black specimens, but the knowledge how to change the 

 colour entirely is still a mystery which is unsolved. 



Leaving the ultimate result, which may possibly require years 

 to work out, I will direct attention to the different shades of colour 

 which are caused by the number and disposition of the dark pig- 

 ment cells contained in the outer skin of fishes. The real colour 

 of the skin or scale may be yellow or transparent, but the distribu- 

 tion of the pigment cells allows only part of the underlying colour 

 to appear. Thus we have different shades of colour, varying from 

 grey-silver, or pale yellow, to deep red, or velvet-black. With this 

 knowledge a considerable number of experiments have been carried 



