342 MARKETABLE BRITISH MARINE FISHES 



larva when hatched is much more advanced in development than 

 those of most fishes with separate floating eggs. The mouth is 

 open, and the yolk much reduced. But a still more striking 

 peculiarity is that while there is as usual a transparent fin-mem- 

 brane along the middle line of the body and tail, there is on the 

 back just behind the head a short thick tentacle arising from a 

 protuberance of the body (Fig. 149). Thus early is the import- 

 ance of the tentacles formed by the dorsal fin-rays indicated. 

 The two pairs of side fins are present as mere skin-folds. 

 Very soon however, when the larva is a few days old, the pelvic 

 or throat-fins begin to lengthen into long tentacles. As the fish 

 grows in size, while the longitudinal fin membrane round the tail 

 region remains unaltered, the tentacle on the back of the head 

 grows larger, and also that of the throat-fin. Then a second 

 tentacle grows out behind the first on the back, and another in 

 the throat-fin (Fig. i 50). The number on the back increases to 

 four, and in the throat-fin to three : they become very long, 

 especially the latter. Now the bony rays of the second dorsal 

 fin and of the ventral and tail fin appear, while the filaments of 

 the throat-fin grow so much that the first is more than twice as 

 long as the body of the fish, and the second reaches to the end 

 of the tail. The breast fin is a large fan-shaped paddle with a 

 circular edge. The fish all this time swims freely near the sur- 

 face or in the open water, not resting on the bottom, and in 

 accordance with this fact the body is as yet narrow from side to 

 side and deep from the back to the belly. The front dorsal 

 tentacles are also long, and it turns out that those first developed 

 are the five hinder ones, the first, which in the adult is shorter 

 than the second, developing last in front of the others. A later 

 free-swimming stage is figured by Dr. Giinther in his Introduc- 

 tion to the Study of Fishes, in which the rays of the throat-fin are 

 somewhat shorter, but still projecting beyond the membrane of 

 the fin, the rays of the enormous breast-fins also project, and the 

 rays or tentacles on the back of the head are furnished with little 

 branched flaps of skin on their sides, except the first which has a 

 forked flap at the end very like that of the adult fish. In this 

 stage the fringed flaps round the edge of the lower jaw have also 

 appeared, the body is broader and flatter, and it is evident that 

 the young fish is gradually passing into the condition of the 

 fully developed angler. 



