644 THE LIVING ANIMALS OF THE WORLD 



their way by means of a horny projection on the lower jaw, and remaining buried at ebb-tide 

 some 5 or 6 inches under the sand, when they are captured by fishermen, armed with rakes, for 

 bait. When swimming in shoals, their presence is often betrayed by schools of porpoises, which 

 feed greedily upon them, preventing their return to the bottom by getting under the shoal, 

 whilst others swim round it. Mackerel also make large raids upon the ranks of such shoals. 



FLAT-FISHES may be reckoned among the most important of food-fishes, and besides are 

 of quite peculiar interest, on account of the remarkable modifications of structure which they 

 have undergone. They differ from all other vertibrates in that, save for the first few weeks 

 of existence, they spend the whole of their lives with one side of the body uppermost the 

 right or left, according to the species. Whether resting or swimming, this position holds 

 good. The newly hatched fish, however, maintains the normal poise of the body, the back 

 being uppermost. Of the many changes which the organs of the body undergo during this 

 strange transformation from a "round" to a "flat" fish, one of the most interesting is that 

 which concerns the eyes. These, in the very young fish, lie one on either side of the head ; 

 but as the fish grows older it begins to lie on its side on the ground, and ultimately, when 

 it is two or three months old, loses the power of sustaining itself in an upright position 

 altogether. The most remarkable feature in this very strange mode of development is, 

 that as the fish comes to lie more and more on its side, so the eye which is undermost 

 begins to move round to the other side, till eventually the two eyes lie side by side on the 

 upper-surface. Strangely enough, in some species the eye moves round the head, passing 

 over its edge, and so to its place beside the stationary eye, whilst in others it acquires its 

 ultimate position by moving through the head, sinking in on one side and appearing again on 

 the other. The coloration of these fishes is also peculiar, in that the two sides are quite 

 differently coloured, the upper side resembling in tone that of the sea-bottom, whilst the under 

 side is pure white. In the young fish, before the habit of lying on one side has been 

 acquired, both sides are coloured alike. The difference in coloration between the two sides of 

 the adult fish appears to be due to the effect of light, since in flat-fishes kept in a tank with 



fl\,t, tj 



K, F.Z.J.] 



HALIBUT 



The largest member of the Flat-fsh Family. The back-fin usually commences much farther forward 



