286 THE ORIGIN OF THE OLDEST FOSSILS, ETC. 



gathered at our door and studied on shore. The water proved to 

 be not only as pure as air, but almost as empty. At high water we 

 sometimes captured a few pelagic animals near the inlets, but we 

 dragged our surface nets through the sounds day after day only to 

 find them as clean as if they had been hung in the wind to dry. 

 The water in which we washed them usually remained as pure and 

 empty as if it had been filtered, and we often returned from our 

 towing expeditions without even a copepod or a zoea or a pluteus. 



The absence of the floating larvae is most remarkable, for the 

 sounds swarm with bottom animals which give birth every day to 

 millions of swimming larvae. The mangrove swamps and the 

 rocky shores are fairly alive with crabs carrying eggs at all stages 

 of development, and the boat passes over great black patches of 

 sea-urchins crowded together by thousands. The number of 

 animals engaged in laying their eggs or hatching their young is 

 infinite, yet we rarely captured any larvae in the tow net, and most 

 of these we did find were well advanced and nearly through their 

 larval life. 



It is often said that the water of coral sounds is too full of 

 lime to be inhabited by the animals of the open ocean ; but this is 

 a mistake, for the water is perfectly fit for supporting the most 

 delicate and sensitive animals, and those which we caught outside 

 lived in the house in water from the sounds better than in any 

 other place where I ever tried to keep them, and instead of being 

 injurious the pure water of coral sounds is peculiarly favourable 

 for use in aquaria for surface animals. 



The scarcity of floating organisms can have only one explana- 

 tion. They are eaten up, and competition for food is so fierce 

 that nearly every organism which is swept in by the tide and nearly 

 every larva which is born in the sounds is snatched by the tenta- 

 cles around some hungry mouth. 



Nothing could illustrate the fierceness of the struggle for food 

 among the animals on a crowded sea-bottom more vividly than the 

 emptiness of the water in coral sounds where the bottom is practi- 

 cally one enormous mouth. The only larvae which have much 

 chance to establish themselves for life are those which are so for- 

 tunate as to be swept out into the open ocean, where they can 

 complete their larval life under the milder competition of the 



