THE LIFE-HISTORIES OF FISHES 169 



growth of the embryo while still in the " uterus " 

 of the parent. Generally it may be said that, the 

 more prolific a fish is, the greater are the destructive 

 agencies at work on the eggs and young ; and con- 

 versely, the less prolific it is, the more perfect are 

 the means securing the nutrition, and safety from 

 enemies, of its offspring. 



Migrations and Habits of Fishes 



Dismissing the very early history of young fishes, 

 we have now to consider the migrations, habits, 

 and food of the adolescent and mature stages. It is 

 very commonly the case that, while the mature 

 adults inhabit the sea at some distance from land, 

 and in relatively deep water, the young forms live 

 near the land, in comparatively shallow waters. It 

 would appear that one reason for this distribution 

 is that there is a richer fauna near the land, 

 and that food is more abundant there. But 

 imperfectly understood physical conditions also 

 tend to produce this contrast in the habitats of 

 the young and mature stages. In the case of the 

 plaice, for instance, it happens that the spawning 

 areas are so situated that the resultant effect of 

 winds, currents, and tides is such as to impel the 

 drifting eggs and larvae towards the shore. So we 

 find that, a month or two after the time when the 

 eggs of this fish may be taken in the tow-nets 

 offshore, the young are present in the shallow 



