644 



The Living Animals of the World 



their way hv means of a lioniy projection on tlie lower jaw, and remaining buried at ebb-tide 

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

 bait. Wlien swimming in shoals, their presence is often betrayed by schools of pwrpoises, which 

 feed greedily upon them, pre\enting tlieir return to the bottom by getting under the shoal, 

 whilst others swinr 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 \ertebrates in that, save for the first few weeks 

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

 rii^ht or left, accordino- to the species. "Whether resting or swimming, this jiosition holds 

 good. The newly hatched fish, however, maintains the normal jioise of the liody, 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 tlie most interesting is that 

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

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

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

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

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

 begins to mo\e round to the otlier side, till eventually the two eyes lie side by side on the 

 upper-surflice. Strangely enough, in some species the eye moves round the head, pjassing 

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

 ultimate posh ion by mo\ing Ikrovgh the head, sinking in on one side and appearing again on 

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

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

 side is pure white. In the young fish, liefore 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 lie due to the effect of light, since in flat-fishes kept in a tank with 



Fholohij W. lianUc-Kt.u, F.Z.S.j 



nA!,TBI-T. 

 Tl.e largest member uf tl.o Flat-fi„l, Family. The baek-fln usually coimuenees mnch taitlier forward. 



[ ildj'urd-uii-^ca. 



