FISHES' EGGS 13 



The specific gravity of floating eggs is just below 

 that of sea-water. Those shown in the illustration 

 were touching one another when put in the photographic 

 tank, but a copepod jumped on to an egg whilst I was 

 focusing, and the weight of this minute crustacean, 

 which is shown magnified eight times, scattered the 

 eggs right and left. 



All fish eggs can be classified under one or other of 

 the types described. 



Among the majority of fishes parental responsibility 

 ceases as soon as the eggs have been deposited, and the 

 eggs are not guarded, nor are the offspring tended. 

 Some fish, however, are extraordinarily zealous in 

 their attentions to the eggs and young, but it is usually 

 the male and not the female that exercises this care. 



The males of several species build more or less com- 

 plete nests, and the perfection of nest-building is reached 

 by the ten-spined stickleback. 



We get the other extreme in the nest of the sand 

 goby, for this fish merely scoops out a hollow under the 

 shell of the scallop as it lies on the bottom. The goby 

 is a most attentive father, although he does not build 

 an elaborate nest, for by a continual movement of 

 his pectoral fins he drives a current of oxygen-laden 

 water over the eggs as they lie under the scallop- 

 shell, and in this manner prevents them from being 

 suffocated. 



To realise how seriously the male fish takes his 

 parental duties, one has but to watch the breeding of 



