GENERAL REMARKS ON THE EGGS OF MARINE FISHES. 17 



An ample margin is thus provided for losses during the 

 development of the embryo and the growth of the young. 

 The pelagic condition of the eggs likewise gives the species 

 a double means of dispersion, which is important when we 

 consider the great areas of the North Sea and the Atlantic 

 that are yet unexplored as regards their food-fishes. The 

 capture of the adults on a large scale can only be carried on — 

 as a rule— in comparatively moderate depths, the deeper waters 

 thus forming a sanctuary, from which may issue eggs and 

 young fishes for the recuperation of the areas which have been 

 thinned. 



One of us' has recently argued for the probability that the 

 pelagic spawning condition is the more primitive, and that the 

 demersal habit has been independently acquired in the later 

 history of the various species which now spawn in that way. 

 The following considerations amongst others were cited in 

 favour of this view : — 



The pelagic-spawning fishes exhibit a greater fecundity, 

 they have a more extended period of ripening and deposition 

 of eggs ; they show no secondary sexual characters, and have 

 promiscuous fertilization. The young in these fishes make 

 the least demand upon their parents (i.e. if we may judge of 

 demand by supply) for nutrition or protection, and are hatched 

 at a much earlier stage of development. Lastly, it is amongst 

 the species with pelagic spawning habit (e.g. the plaice) that the 

 larval and post-larval migration is most marked, the demersal 

 types forming a series (from herrings to small littoral forms) 

 in which the early stages are as it were telescoped up and the 

 migration thereby eliminated from the life-history. 



The pelagic eggs are deposited by the parents in the water 

 and there fertilized. They are very little lighter than sea 

 water and hence rise slowly towards the surface of the ocean, 

 when their development proceeds till the capsule is burst by 

 the little larva, which then emerges from its confinement. These 

 eggs are all beautifully translucent, a fact which combined 

 with their small size no doubt saves an immense number of 

 them from destruction, as their presence even in a small 

 ' A. T. Masterman. Op. cit. 

 M. F. 2 



