CHAPTER III 



THE GENERATION OF FISHES AND THEIR FECUNDITY 



The generative organs of fishes differ considerably in different 

 classes and orders. In skates and dog-fishes (Fig. 29) they 

 resemble closely those of birds. In the female the ovary, or organ 

 where the eggs are produced, is a lobed mass at each side of the 

 body cavity, and attached to the dorsal wall of that cavity. The 

 eggs when mature are very large, and in adult specimens a 

 number of them of various sizes and stages of development are 

 seen bulging out from the surface of the ovary. These eggs when 

 ripe burst through the surface and become free. They are round 

 balls of yellow yolk, of considerable '.size, larger in some species 

 than in others, but not very much larger or smaller than the yolk 

 of a hen's egg. Running along the back of the abdominal 

 cavity is a fleshy tube, the egg-tube or oviduct. This tube is 

 open at both ends. Inside the body its open front end is situated 

 at the side of the gullet in front of the liver. Its hinder end 

 leads into a sac which opens to the exterior at the vent. The 

 eggs must get into this tube, and pass down it, before they can 

 escape from the fish. They are taken up into the opening at its 

 front end, swallowed as it were by the egg-tube, and pi-essed down 

 it by the movement of its sides. Towards the upper part of this 

 tube is a ring-like thickening, and here the tough horny shell is 

 formed. The upper end of the oviduct usually contains some of 

 the milt of the male, introduced during the union of the sexes, 

 which takes place from time to time as in higher animals. By 

 the action of this milt the germ in the yolk is fertilised. At the 

 same time a certain quantity of clear sticky liquid, the " white," is 



