278 THE ORIGIN OF THE OLDEST FOSSILS, ETC. 



and small animals, but these things cannot be the food-supply of 

 the ocean, for no carnivorous animal could subsist very long by 

 devouring its own children. The total amount of these animals is 

 inconsiderable, however, when compared with the abundance of a 

 few forms of protozoa and protophytes, and both observation and 

 deduction teach that the most important element in marine life 

 consists of some half-dozen types of protozoa and unicellular 

 plants ; of globigerina and radiolarians, and of trichodesmium, 

 pyrocystis, protococcus and the coccospheres, rhabdospheres, and 

 diatoms. 



Modern microscopic research has shown that these simple 

 plants, and the globigerinae and radiolarians which feed upon them, 

 are so abundant and prolific, that they meet all demands and 

 supply the food for all the animals of the ocean. This is the fun- 

 damental conception of marine biology. The basis of all the life 

 in the modern ocean is found in the micro-organisms of the surface. 



This is not all. The simplicity and abundance of the micro- 

 scopic forms and their importance in the economy of nature show 

 that the organic world has gradually taken shape around them as 

 its centre or starting-point, and has been controlled by them. 

 They are not only the fundamental food-supply but the primeval 

 supply, which has determined the whole course of the evolution 

 of marine life. The pelagic plant-life of the ocean has retained 

 its primitive simplicity on account of the very favourable character 

 of its environment, and the higher rank of the littoral vegetation 

 and that of the land is the result of hardship. 



On land the mineral elements of plant-food are slowly supplied, 

 as the rains dissolve them; limited space brings crowding and com- 

 petition for this scanty supply ; growth is arrested for a great part 

 of each year by drought or cold ; the diversity of the earth's sur- 

 face demands diversity of structure and habit ; and the great size 

 and complicated structure of terrestrial plants are adaptations to 

 these conditions of hardship. 



At the surface of the ocean the abundance and uniform distri- 

 bution of mineral food in solution ; the area which is available for 

 plants ; the volume of sunlight and the uniformity of the temper- 

 ature are all favourable to the growth of plants, and as each plant 

 is bathed on all sides by a nutritive fluid, it is advantageous for the 



