BEEEDING-HABITS OF SOME WEST-AFRICAN FISHES. 127 



long cylindrical bag, attached somewhat far behind for a Teleostean, and covered with 

 a vascular network (PI. XI. figs. 4 & 5). 



The tail is from first to last perfectly diphycercal, and is at first provided with 

 a dorsal and a ventral fin-fold reaching right to the tip of the tail. 



Before leaving the nest, both outer gill-filaments and yolk-sac are absorbed and the 

 mature form is reached. 



Immediately after hatching, the larvge commence their characteristic movements, 

 throwing the head and fore part of the body from side to side incessantly. The larvae 

 are at first so small in proportion to the size of the yolk-sac, that they are quite unable 

 to move it. By this constant movement the larvae tend towards the surface, and the 



Text-fig. 20. 



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Floating nest of Gymnarchus. 



weight of the yolk tending downwards, the yolk-sac becomes gradually drawn out into 

 the long appendage already mentioned. About three days after hatching, the larvae are 

 strong enough by their movements to raise the yolk-sac off the bottom of the nest for a 

 moment, but it is quickly drawn back by its weight. 



By the tenth day after hatching, the larvae are able to drag their yolk-sac to the 

 surface of the water, when they take a gulp of air into their lung-like swim-bladder 

 and fall again to the bottom, on reaching which they again start for the surface with 

 unceasing regularity, so that when looked at from above the nest of Gymnarchus, 

 with its swarm of scarlet-bearded, yolk-hampered larvae, presents a most amazing 

 spectacle. 



By the time the huge yolk-sac has been completely absorbed, the young larvae are 

 ready to leave the nest. They still, however, continue their ceaseless journeyings to 

 the surface for air. It may now be noticed, however, that the passage back to the 

 bottom of the nest is not merely a passive falling, but that the young larvae actually 



