THE FLAT-FISH FAMILY 211 



Of these eighteen kinds all are used as food except five, 

 namely, the solenette, the scald-fish, and the three topknots. 



All the flat-fishes possess in a remarkable degree the power 

 which is present in all fishes, of changing their colour, or the 

 intensity of their colour, in accordance with the tone of their 

 surroundings. On a light sandy ground they become pale, on a 

 •dark muddy ground they become almost black. Their habits 

 have been sufficiently described in a previous part of this book. 



The eggs of all the British flat-fishes are of the buoyant and 

 separate kind, but it has recently been discovered that those of 

 an American species, the winter flounder {Pseudopleiironectes 

 Americaniis), are heavy and adhesive, and are best treated in 

 the hatchery by being spread on panes of glass. This fish 

 resembles the plaice and dab, having rough scales like the latter. 

 In Europe even the flounder, which lives chiefly in brackish or 

 nearly fresh water, produces floating eggs, and goes down to the 

 sea to spawn. It is a curious fact that the eggs of most of the 

 right-sided species, plaice, dab, flounder, lemon dab, witch, 

 halibut, and long rough dab, are without an oil globule, while 

 those of all the left-sided species, from turbot to Norwegian 

 topknot, have a single oil globule. The eggs of the soles have a 

 number of small oil globules. 



The common character of the newly hatched larvae is that 

 the intestine ends immediately behind the yolk, and opens on 

 the edge of the fin-membrane. In other respects the larvae of 

 the flat-fishes are very much like those of equal-sided fishes, and 

 at first they swim near the surface and feed on the minute float- 

 ing creatures in the same way. 



Mention has already been made, in the first part of this book, 

 of the fact that the peculiarities in the position of the e}-es and 

 in the habits of flat-fishes are acquired when they are still very 

 small, during the transformation of the larva to the adult condi- 

 tion. The mode in which the extraordinary position of the eyes 

 was brought about gave rise, when the transformation of the 

 larvae was first discovered, to a lively controversy. 



A good many years ago the Swedisli naturalist Malm, whom 

 I have previously mentioned, noticed small turbot, plaice, and 

 other flat-fishes in which the eyes were not both on one side 

 of the head, but in various positions which seemed to show that 

 one eye was gradually moving round to the other side, passing 



P 2 



