THE HAUNTS OF LIFE 79 



and more generations are living at the same time. In 

 some cases the large number of different species, within 

 a relatively narrow radius, is very characteristic. Thus 

 there are over 5,000 species of Radiolarians. This, per- 

 haps, means that the conditions of life are relatively easy 

 and Natural Selection not very stringent. 



There is much still to learn in regard to the vital economy 

 of the sea, for instance as to the food supply. It has 

 been calculated by Putter and Dakin that the ' producers ' 

 (the plant-plankton) are often insufficient for the ' con- 

 sumers ' (the animal plankton), and Dr. Dakin has also 

 maintained that, even if there were enough of food, it 

 would be ' an altogether unthinkable piece of work ' for 

 the animal to catch enough to cover its physiological 

 expenditure. Dr. Dakin calculates that a sponge sixty 

 grammes in weight would require to filter several thousand 

 times its own volume of water per hour in order to obtain 

 sufficient food, which sounds a somewhat formidable 

 task. A big jellyfish, he calculates, would require over 

 seven millions of nauplius larvae per day, which is literally 

 a large order. ' It is quite impossible for such large quanti- 

 ties to be caught, and equally strange that remains of the 

 creatures are so rarely found, if they have been captured 

 as food '. Perhaps it is too soon, however, to be very 

 confident in regard to the amount of organic material that 

 a creature like a sponge or jellyfish requires to cover the 

 loss due to its metabolism. 



Prof. Piitter's view is that many marine animals are 

 in a way saprophytic feeding on the organic compounds 

 contained in solution in the water. He regards the sea 

 as a great reservoir of dissolved foodstuffs (compounds 

 of carbon other than carbonates, and compounds of nitrogen 



