84 THE SEAS 



in which case they swim over the bottom truly on their 

 stomachs. 



The 3'oung stages of many fish are totally unlike the 

 adults. The Angler Fish, for instance, so shapeless and 

 cumbersome when grown up, is a most beautiful object 

 soon after hatching (Plate 37). Its fins are drawn out 

 into filaments of fairy-like delicacy. Like other young fish, 

 the Angler spends its early days drifting in the water layers 

 above the bottom, and the long-drawn-out filaments of the 

 fins help to keep it suspended in the water. 



Migrations 



It is obvious that, if, for several weeks in the early 

 stages of their lives, most fishes are going to drift freely 

 about at the mercy of tide and current, they will be carried 

 far from where their parents shed the eggs. The greatest 

 importance therefore attaches to the position of the 

 spawning ground, from which after a definite time the 

 young fishes must have been carried to suitable grounds for 

 feeding and growing. For this reason many adult fishes 

 undergo spawning migrations, that is, they move off all 

 together to a chosen locality to shed their eggs. The plaice, 

 for instance, in the southern North Sea move further south 

 (Fig. 61, p. 323), so that their eggs and young are drifted by 

 the prevalent currents on to the so-called " nurseries " in the 

 shallow, sandy bottomed regions along the coasts of 

 Holland. The herring, too, move in from deeper water to 

 deposit their eggs on the bottom in certain regions, and it is 

 then that the fishermen set to work to catch them in the 

 drift nets. 



But most surprising of all spawning migrations is that of 

 the common fresh-water eel. For years men in all countries 

 of Europe have wondered how it is that the eels in our 

 streams thrive and multiply, and yet nobody had ever seen 



