DRIFTING LIFE 115 



grass being eaten by man ; so also in the sea, the ultimate 

 food supply is to be found in the drifting microscopic 

 plants. But, whereas on land the plants are substantial 

 and can be directly eaten by large animals, in the sea they 

 are minute and are first eaten by the small drifting animals, 

 which are in turn swallowed by larger creatures, and so on 

 until, eventually, the fish forms food for man. In fact 

 certain chemical constituents of our food have been traced 

 to these tiny plants. To most the word " vitamin " is 

 well-known. It is the name given to certain chemical 

 bodies, which, although present in minute quantities only 

 in our food, appear to be essential to our health and well- 

 being. Their absence is thought to give rise to such diseases 

 as scurvy ; and fierce controversy has raged over the 

 desirability of eating white or wholemeal bread. Cod-liver 

 oil also contains a certain vitamin which is thought to be 

 partly responsible for its great medicinal value. The 

 presence of this vitamin has been traced from the liver of 

 the cod to the insides of the capelin (Mallotus villosus), a 

 little fish that forms a large portion of the cod's food, and 

 the swarms of which bring the cod together in vast shoals 

 on the Newfoundland banks. From the capelin it has been 

 traced to the minute animals on which it feeds, and so to the 

 diatoms which nourish them. It is in these little plants — 

 the diatoms — that the vitamins are made. 



Plankton Animals 



We have mentioned above that the drifting plants form 



the chief food of the small animals of the same community. 



Of what is this animal population chiefly composed ? 



Actually almost every group of the invertebrate animal 



kingdom has representatives in the plankton. In addition, 



the young of many kinds of fish live for a shorter or longer 



period a free, drifting existence. But of far the greatest 



I 



