98 



MARKETABLE BRITISH MARINE FISHES 



Fig 



49. — A single globule 

 of Noctiluca. 



naturalists Noctiluca, or " night-light." They are among the 

 principal causes of the phosphorescence of the sea. The scum 

 they form has usually a salmon-pink colour. 



There arc a few cases in which floating eggs instead of being 

 free and scattered are enclosed in large numbers in a single sheet 

 or mass of transparent jelly-like substance. The spawn of the 



frog-fish or angler {LopJihis piscatoriiis), 

 for instance, was found by Prof. Alex. 

 Agassiz in America to form an im- 

 mense gelatinous band from two to 

 three feet broad and twenty-five to 

 thirty feet long. Each o:^^ has a 

 simple yolk and a single oil-globule, 

 and the band is formed of the eggs 

 of a single female sticking to one 

 another by the surfaces of their en- 

 closing membranes, the whole floating 

 free in the sea. The band or ribbon 

 does not always float at the surface. 

 A portion of one was brought up in a 

 In British waters it has been obtained 

 more than once. A quantity was once brought alive to the 

 Plymouth Laboratory, and it has been taken on the coast of 

 Scotland. 



When the eggs of the bony fish are laid they have not been 

 fertilised, and the young fish have not begun to develop in them. 

 It has been explained that they come into contact with the male 

 generative substance in the water, and that one of the sperms 

 enters each ^g'g through the micropyle and penetrates into the 

 germ. Before the &^^ is shed, when it is taken in a perfectly ripe 

 condition from the roe of the female, the membrane is in contact 

 with the contained substance, and the germinal matter forms a thin 

 layer all round the yolk. Whether the o.^'g is fertilised or not, 

 certain changes take place in it when it passes into the sea-water. 

 The membrane separates from the Qg,^, and the germinal matter 

 collects into a mass on one side of the yolk. If the Oi-gg is not 

 fertilised no further changes occur in it ; after a time it dies and 

 then putrefies. But if it is fertilised then a further process of 

 change goes on which converts the o^gg into a young fish. This 

 process is called the development of the fish. We may consider 



trawl in Mount's Bay. 



