SCALES, MIRRORS, LEATHERS 



but always exceptionally, certain specimens affected by 

 this difference in the scaly structure which makes 

 them ' mirrors ' or ' leathers '. Breeders, who noticed 

 that these particular specimens were usually larger than 

 the others, decided to pick them out. So it was that 

 these privileged kinds were secured, these kinds which 

 grow rapidly. And, as you know too, the characteristic 

 disappears as it came. If there is any break in the 

 constant selection of qualified reproducers, in a few 

 generations the carp return to their original dress of 

 scales, and the meagre size which goes with it." 



" I know," he said. " I remember how, during the 

 last century, certain precocious types were created by 

 such a process of selection. But what I don't know, 

 and what I am asking you, is how there can be any 

 relation between the change in the scales and the 

 rapidity of growth. Please note," he added, " I don't 

 ask you why this connection exists; I shall be quite 

 content if you will tell me how." 



" Even if we keep the question within such limits," 

 I replied, " it is fairly searching. It is much more 

 complex than it seems on the surface, and we do not 

 know all the facts that we shall have to know before 

 it can be answered. It may be that several causes 

 come into play, and not one only. The processes of 

 life are so many and so intricate, causes and effects 

 at one and the same time, that we cannot be perfectly 

 certain about them. As a matter of fact, this change 

 that takes place in the scaly covering is the consequence 

 of a diminution in the assimilation of the mineral salts 

 which go to build up the skeleton; it is a corollary of 

 the presence of shorter and softer bones. Here we 

 are reminded of what happens in the cartilaginous 

 fishes, whose growth is more rapid than that of the 

 bony fishes. It may be, further, that a bare skin lends 

 itself more readily to the processes of assimilation. Or 

 can it be that the process of feeding and that of 

 digestion have dissimilar capacities? Here we are 

 ioo 



