24 GENERAL REMARKS ON THE EGGS OF MARINE FISHES. 



the bony fishes into two divisions according to the character of 

 their eggs (either pelagic or demersal) we at once note that this 

 character by no means agrees with the characters of the adult 

 fishes which determine their relationships ; thus we note for 

 example that the sprat has a typical pelagic egg, and its 

 close ally the herring, so close that their young forms are 

 hardly distinguishable, has a demersal egg, laid in clusters 

 upon gravel, seaweeds and zoophytes. This and other instances 

 point to the fact that the pelagic or demersal habit is not 

 determined by the general structure of the adult but by 

 other factors. 



Quite the same absence of connection occurs between the 

 size of pelagic eggs and that of the adult, the turbot for 

 instance having a smaller egg than the plaice, and the cod than 

 the whiting, although the greater size of the turbot and the cod 

 when compared with the plaice and whiting must be familiar 

 to all. On the other hand the size of the eggs seems in some 

 measure to vary inversely as the number, as will be seen by 

 comparing the cod and the whiting. Too much reliance however 

 must not be placed upon this comparison. 



Lastly, the oil-globule does not by any means characterise 

 one particular group of fishes, the closest allies differing in this 

 respect ; the single instance of the turbot's egg with its oil- 

 globule and that of the plaice with none must here suffice. 



The study of the development of food-fishes furnishes 

 one with beautiful examples of what is known as convergent 

 evolution. 



The most important demersal egg amongst the food-fishes 

 is certainly that of the herring. This is attached so securely to 

 the structures on the bottom or to the bottom itself that so far 

 as experience goes it is never tossed on shore or brought up by 

 the trawl in the ordinary course of work. The eggs have a firm 

 capsule coated with an adhesive substance which fixes them 

 firmly to each other and to foreign surfaces. The adults, which 

 show a remarkable persistence in attaining their spawning 

 grounds, take, like the salmon, no further heed of them after 

 deposition and fertilization. In some cases, however, the eggs 

 are tended by both or by one of the parents. The well-known 



