THE FLAT-FISHES 239 



burnished sheen so noticeable in the flat-fish. With the 

 single; exception of the orange-red spots in the plaice, there 

 is not a touch of any colour other than browns and greys 

 in any full-grown flat-fish, though the larval stages show traces 

 of brighter tints. 



Another curious point about the fish of this sub-order is 

 the great difference in their distribution. It might have 

 been thought that so homologous a group of animals would 

 have been characteristic, if not of any particular locality, at 

 any rate of cold or warm seas. In closely related flat-fish, 

 however, we find a northern and a southern habitat side by 

 side; and this is well illustrated by the case of the three 

 topknots, two only of which are found in extreme northern 

 waters, and one only of which extends to the Mediterranean, 

 while of the first two one extends as far south as the Bay of 

 Biscay, and the other no farther than the English Channel. 



All of the flat-fish, at any rate on our coasts, deposit floating 

 eggs, and many of them proceed for the purpose some distance 

 from land. This can hardly be, as has been suggested, in 

 order that the greater pressure at those depths shall assist in 

 the extrusion of the egg,* for the sole, which in natural 

 conditions spawns in moderately deep water, has frequendy 

 deposited its eggs in the tanks of the aquarium. The instinct 

 which prompts these fish, then, to migrate seawards when 

 ready to reproduce their species is far more probably one of 

 self-defence, for they know that the spawn-eating surface fish 

 are much more abundant in the waters immediately beside the 

 land. Not only other fishes moreover, but also nature would be 

 against them in the shallows, where the constant disturbance 

 of the water by breaking waves would obviously prejudice the 

 quiet development of the egg and subsequently of the larva, 

 while a storm might actually have the effect of flinging both 

 ashore. 



The eggs of the turbot group, it will have been noticed, 

 * See also remarks on Conger spawning in captivity, p. 182. 



