VARIATION 369 



coloured pigment everywhere visible ; this variation is called 

 xanthochroism. When the coloured pigment is also wanting 

 the fish is silvery. Besides the uniformly coloured varieties 

 many others occur among gold-fishes, as may be seen in any 

 pond where numbers of these fish are kept : some are black and 

 silver, some black and red. These conditions are closely similar 

 to the various uniformly coloured and pied variations seen in 

 domesticated mice, rabbits, etc. ; in both cases the absence 

 of all pigment, or albinism, occurs, either in part or all of the 

 skin. The variety of gold-fish known as the telescope fish is 

 distinguished by extraordinary monstrosities of the eyes and 

 caudal fin ; the former are situated on outgrowths of the head 

 like stalks, reminding one of the eyes in crabs and other stalk- 

 eyed Crustacea, while the fin is doubled or split ventrally and 

 the two halves are spread out horizontally or in the form of an 

 inverted V. The telescope fish is reared principally in Japan 

 and probably breeds true, but doubling of the tail-fin, absence 

 of the dorsal and other abnormalities, occur frequently among 

 specimens bred in Europe. Sir R. Heron in 1841 stated that 

 the abnormal fish did not produce a greater proportion of ab- 

 normal offspring than the normal fish, but it seems probable 

 that the inheritance of these mutations would be found to be 

 Mendelian. Gold-fish were kept in China at a very early 

 period and were introduced into Europe in the seventeenth or 

 eighteenth century. 



The common carp, Cyprinus carpio, which is distinguished 

 by the possession of four barbels on the upper lip, is also a native 

 of China and other parts of Asia. It has been kept in a 

 domesticated state in China from ancient times and was intro- 

 duced into Germany and France in the thirteenth century. In 

 Germany, where until recently the supply of marine edible 

 fish was limited to the coast, the cultivation of the carp has been 

 continued to the present time ; in England, in the middle ages, 

 it was kept in ponds by the monks as a supply of fish for Lent 

 and Fridays, but its cultivation in this country has long been 

 abandoned. In Germany among cultivated carp several dis- 

 tinct varieties have arisen. One of these is called the mirror- 

 carp, and is distinguished by the greater size and lustre of the 

 scales ; it has a small head and a thick body and grows to a 

 large size ; some varieties of the mirror-carp have the scales 



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