GENERATION OF FISHES AND THEIR FECUNDITY 



73 



effect the fertilisation of each egg, the great number are only 

 advantageous in securing that every egg shall be fertilised. 



In the herring the hard roe of the female and the soft roe of 

 the male are both smooth outside, and both equally large. But 

 although their connections and their mode of construction arc 

 essentially the same in other fishes their appearance and size are 

 in many cases' very different. In the flat fishes such as the 

 plaice, sole, turbot, &c., the soft roe of the male is much smaller 

 than the hard roe of the female. The latter has its opening in 



A 



B 



FIG. 33. Sperms of various fishes, highly magnified. A, those of the Thornback 

 Ray ; B, of the Herring ; C, of the Pike ; D, of Plaice or Sole. Each side of 

 the squares represents yoVcr inch. 



front of the ventral fin, not far behind the head, and extends 

 back on each side beneath the flesh of the body, nearly to the 

 root of the tail. The soft roe, on the contrary, is a small white 

 mass at the "back of the central cavity of the fish. The 

 difference in size between the male and female roes is greatest in 

 the sole, and their appearance and position in this fish are clearly 

 shewn in the four illustrations here given. Fig. 34 represents the 

 appearance of the belly cavity of a female sole laid open by the 

 removal of the skin and flesh covering that cavity on the upper 



