CHAPTER V 

 Drifting Life 



We have dealt so far with those animals and plants which 

 live either on the sea bottom, or swimming actively through 

 the water above the bottom. There is yet another com- 

 munity of organisms in the sea whose existence is, perhaps, 

 not generally realized. It consists of countless numbers of 

 animals and plants which drift about in the water layers 

 at all depths between the sea surface and the bottom, at the 

 mercy of tide and current. They are nearly all small, 

 most of them minute, and many only visible under the high- 

 powered microscope. 



It is extremely easy to demonstrate their presence ; it is 

 merely necessary to drag through the sea for a few minutes 

 a small cone-shaped net, or " tow-net " (Plate 96), made 

 of fine muslin, cheesecloth or silk ; or, if one is on an ocean 

 liner, it is even possible to obtain them by hanging a small 

 muslin bag under the salt water tap in the bathroom and 

 just letting the water run. 



At times this drifting life is so abundant that it colours 

 the sea for miles around. Such expressions as " red 

 water," " yellow water," and " green water," are used by 

 fishermen, who become wonderfully expert at deciding 

 where to shoot their mackerel or pilchard nets by slight 

 differences in the tint of the water that landsmen would 

 not notice. In every case the characteristic tinge given 

 to the sea 13 known to be due to the presence of certain 

 kinds of organisms in innumerable quantities. Darwin 



no 



