94 MARKETABLE BRITISH MARINE FISHES CHAP. 



been more than once described ; they have been obtained in 

 the open Atlantic in tropical latitudes, and probably belong 

 to flying-fishes. 



After fertilisation the egg-membrane in the eggs of all bony 

 fishes separates from the yolk mass within it, and at the same 

 time the germinal matter collects together and forms a mass 

 lying upon the yolk. The proportion which the mass of germinal 

 matter bears to that of the yolk varies considerably, in the 

 herring the former is nearly as large as the latter, but usually it 

 is very much smaller. In the eggs hitherto mentioned the yolk 

 consists of a number of globules of various sizes, held together 

 by a network of strands connected with the germinal mass. In 

 most cases there are also a few globules of a different kind, 

 consisting, in fact, of oily matter, at the surface of the yolk mass. 

 In consequence partly of the granular nature of the yolk and 

 partly of its separation into these numerous globules, adhesive 

 and heavy eggs are not very transparent, although generally 

 sufficiently so to allow of the embryo and internal parts of the 

 egg being seen to some extent in the living condition of the egg. 

 Herring eggs are rather more transparent than the majority of 

 adhesive eggs. 



The third kind of eggs, those which float about in the sea, are 

 remarkable for their great transparency. It is difficult to dis- 

 tinguish them when present in small number in a bottle of clean 

 sea-water. This is due partly to the transparent character of 

 the yolk itself, partly to the fact that it is not disposed in a 

 number of separate globules, but usually forms a single undivided 

 mass surrounded by germinal matter in a thin layer on the out- 

 side. The character of a typical floating egg, such as that of 

 the cod or plaice, is shown in Fig. 45. All the parts of the egg 

 are clearly seen when it is examined in the living condition with 

 the microscope. After death and when preserved in the liquids 

 used by naturalists for the purpose the eggs become opaque. 

 The egg is made up of the membrane surrounding it, and the 

 mass of the egg proper, consisting of the germ, G, and the yolk,. 

 Y. In such an egg there are no oil-globules and no divisions in 

 the yolk. The following are the fishes which are known to have 

 such eggs, the spawn of each of them having been examined by 

 naturalists cod, haddock, whiting, bib, poor-cod, pollack, coal- 

 fish, plaice, flounder, dab, lemon sole or merry sole (PI. micro- 



