42 MARVELS OF FISH LIFE 



bottom. At first the yolk sac fills up most of the egg 

 case, but as time goes on the embryo ray absorbing the 

 food from the sac grows in size, and the sac diminishes 

 in proportion. 



In the photograph of embryo thornbacks removed 

 from the egg case, the growth of the young fish at the 

 expense of the yolk sac is well illustrated. 



As soon as a fish hatches, it enters upon the larval 

 stage, and, as will be seen later, the appearance of the 

 larvse of bony fishes, such as the salmon, roach and 

 plaice, is totally unlike the parent fish, and the yolk 

 sac is only partially absorbed when they leave the egg. 

 The ray, however, when he emerges from the egg case 

 is a perfectly formed fish, and very little remains of the 

 sac. The back is already coloured and marked so as 

 to render him inconspicuous on the bottom, and protect 

 him while he is still of tender age. 



The under-surface is colourless, for lying on the 

 bottom there is no need for this part to be concealed. 

 The yolk sac has practically gone, the fins are as they 

 will appear in after life, and the mouth being open, the 

 young ray is able to feed at once. The gill slits are seen 

 on each side of the middle line, between the mouth and 

 the remains of the yolk sac. At fourteen days old the 

 black spots seen on the back of the newly hatched ray 

 blend together, and give it a more uniform shade. 



The top photograph of the second plate shows a 

 ray three weeks to a month old, and it will be seen that 

 there are several rings round the edge of the large fins. 



