104 MAKKKTAr.l.K IIRITISH MAKIXK I ISIIES CHAP. 



the tail into the shape of an S, and then suddenly straightening 

 it. It is however very difficult to rear them completely in 

 confinement, and the successive stages of the various kinds of 

 fish have to be patiently and laboriously traced by comparing 

 specimens caught by fine nets in the sea. 



The great and important change which takes place in the 

 larva; after they begin to feed is the development of the bones 

 of the skeleton, connected with which is the formation of the 

 permanent fins. During this further development considerable 

 changes of form and habit take place, which are different in 

 different kinds of fish. The fin-rays are bony rods and develop 

 at the same time as the rest of the skeleton, and, the fish being 

 in most cases still very transparent when alive, the changes that 

 take place can be plainly seen. 



The transformation of the larva with its continuous fin- 

 membrane, after the absorption of the yolk, into the young 

 cod with its three dorsal and two ventral fins is illustrated in 

 Figs. 56-58. 



At the later stages of the transformation the little fish ceases 

 to be transparent, its flesh becomes thicker and denser, and the 

 skin becomes pigmented or silvery, and finally the scales, if 

 there are any, or other minor peculiarities of the perfect fish, arc 

 developed. For the details of these changes in various species, 

 so far as they have been studied, reference must be made to the 

 figures and descriptions of particular fishes given in the second 

 part of this work. One or two special cases may be mentioned 

 here. The young herring in its intermediate stages is remark- 

 able for its great elongation and slender form, and its dorsal fin 

 is situated towards the tail, much further back than in the fully 

 developed fish. The most surprising transformation is that of the 

 flat-fishes (Figs. 59-62), the larvae of which swim upright and are 

 very similar to the larvae of the cod or other fishes of the cocl 

 family. When the fin-rays develop in these fishes their ex- 

 ceptional character is at once shown by the extension of the 

 dorsal and ventral fins along nearly the whole length of the 

 dorsal and ventral edges, and by the great breadth and thinness 

 which the body acquires. But during this part of the develop- 

 ment a most remarkable change occurs : the eyes are at first 

 opposite to each other, one on each side of the head, as in cod, 

 mackerel, or other fish, but when the fin-rays develop one of the 



