W. K. BROOKS ON THE GENUS SALPA. 147 



On one occasion the Challenger steamed for two days through a 

 dense cloud formed of a single species, and they are found in all lati- 

 tudes from the arctic regions to the equator, in masses which discolor 

 the water for miles. We know, too, that they are not restricted to the 

 surface, and that the banks of copepods are sometimes a mile thick. 

 When we reflect that thousands would find ample room and food in 

 a pint of water, we can form some faint conception of their universal 

 abundance. 



* 



TJie Primary Food-supply. 



As the result of our review, we find that the organisms which are 

 visible without a microscope in the water of the ocean and on the sea 

 bottom are almost universally engaged in devouring each other, and 

 many of them, like the blue-fish and the albacore, are never satisfied with 

 slaughter, but kill from mere sport. 



Insatiable rapacity must end in extermination unless there is some 

 unfailing supply, and as we find no visible supply in the water of the 

 ocean we must seek it with a microscope. By its aid we find a wonder- 

 fully rich and diversified fauna made up of innumerable Iarva3 of all 

 sorts of marine animals, together with a few minute and simple metazoa, 

 but these things cannot form the food-supply of the ocean. It is clear 

 that a single carnivorous animal could not exist very long by devouring 

 its own children, and the result must be the same however great the 

 number of individuals or species. 



The total amount of these organisms is inconsiderable, however, 

 when compared with the abundance of a few forms of protozoa and 

 protophytes, and both observation and deduction force us to recognize 

 that the most important element in the total amount of marine life 

 consists of some half-a-dozen types of protozoa and unicellular plants, of 

 giobigerina and radiolarians, and of trichodesmium, pyrocystis, pro- 

 tococcus, and the coccospheres, rhabdospheres and diatomes. 



Modern microscopic research has shown that these simple plants, 

 and the globigerina3 and radiolarians which feed upon them, are so 

 abundant and prolific that they meet all the demands made upon them 

 and supply the food for all the animals of the ocean. 



This is the fundamental conception of marine biology. The basis of 

 all the life in the modern ocean is to be sought in the micro-organisms 

 of the surface. 



This is not all. The simplicity and abundance of the microscopic 



