164 BRITISH FISHERIES 



about two inches in length and one inch broad, and 

 corners are produced to form horns. Within 

 these cases were the soft eggs proper, which 

 consist, when the egg is alive, of a large mass of 

 yellow yolk, on the surface of which is the blasto- 

 derm, or formative material of the embryo, or, it 

 may be, the partially developed embryo skate itself. 

 The eggs of the dog-fish are somewhat similar, but 

 are more elongated, and the corners of the case are 

 produced into long twisted cords. The live eggs 

 of skates and dog-fishes can generally be procured 

 only from the bottom of the sea, in water from five 

 to twenty fathoms deep, by means of dredging. 

 They too are heavier than sea-water, and sink to the 

 bottom when emitted by the mother. 



Impregnation and Development 



In the case of these Elasmobranch fishes there is 

 an actual physical connection between the sexes at 

 the breeding season, and the eggs are impregnated 

 while still within the oviduct of the female, and 

 before the horny egg-capsule has been formed. In 

 the Teleost fishes, whether they produce pelagic or 

 demersal eggs, this connection is only an indirect 

 one ; eggs and spermatozoa are shed by males and 

 females into the sea at the same time. Whether 

 the spermatozoa reach the eggs fortuitously, or 

 whether there is some obscure attraction between 

 these sexual elements, we do not know, but at 



