GYMNAECHTJS. 77 



deepest part of the nest was opposite to that side where the wall was low, the bottom 

 being about six inches below the surface of the water. 



" In this nest were deposited about a thousand spherical amber-like eggs 10 millim. 

 in diameter. The eggs hatched five days after being laid, and in eighteen days a 

 thousand young fry of Gymnarchus niloticus left the nest when three inches long. 



" Though there are many interesting features in the development of these eggs, I do 

 not intend to deal with them in detail here, but merely to mention that the development 

 is exceedingly shark-like. The larvae soon after hatching develop extremely long 

 gill-filaments, which hang down in two blood-red bunches from the gill-arches, of 

 which there are four. The yolk-sac, at first spherical, later becomes drawn out into a 

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



Ym. 10. 



Larva of Gymnarchus niloticus, six days after hatching. (After Budgett.) 



a vascular network. 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 larvae 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 

 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 



