GENERATION OF FISHES AND THEIR FECUNDITY 



65 



among sea-weed not far from low-water mark, where at 

 low tide they can be gathered by 

 hand. Besides the two spotted species 

 there is only one other occurring in 

 British seas which lays eggs, namely, the 

 black-mouthed dog-fish {Pristiuriis mel- 

 anostoina), and this species, which is 

 abundant in the Mediterranean, has been 

 very rarely taken off our coasts. The 

 rest of the British sharks and dog-fishes 

 produce their young alive. All the 

 ordinary skates and rays, on the other 

 hand, lay eggs which differ only in size 

 and minor peculiarities in the different 

 species. The electric ray {Torpedo), the SP 

 eagle-ray {Alyliobatis) and the sting-ray 

 [Trygon) bring forth their young alive. 

 There is no evidence at present to show 

 that the egg-laying rays seek particular 

 localities in which to deposit their eggs. 

 The eggs are occasionally taken in the 

 trawl or dredge, and the empty shells 

 are often cast ashore. They are some- 

 times called mermaids' purses. 



In the majority of the bony fishes 

 the condition of the roes and the mode 

 in which the eggs are produced and 

 fertilised are quite different. If we take 

 the herring as an instance, it is well 

 known that in this fish (Fig. 30) there 

 is a hard roe or soft roe on each side 

 of the body cavity, and that in the 

 spawning season these are very large so 

 that the abdomen of the fish is distended ^'t, „^°--X^AT^r' °^ \ ^'' 



ring with its body cavity laid 



by them. The roe or hard roe occurs open at the lower edge, to 



in the female fish and contains the eggs 



or spawn, the milt or soft roe belongs 



to the male and contains the white 



milky liquid which must act upon the 



eggs before they can develop. Careful 



show the roes and intestines, 

 &c. L. liver, in front of 

 which is seen the heart ; S. 

 the stomach; I. the intestine; 

 SP. the spleen ; O. the roes 

 or milts opening together 

 behind the opening of the 

 intestine. 



