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 les 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 
