582 A NATURALIST ON THE "CHALLENGER." 



various kinds washed down by rivers, or floated out to sea from 

 ♦ shores and sunken to the bottom when water -logged. 



The dead Pelagic animals must fall as a constant rain of 

 food upon the habitation of their deep-sea dependants. Maury, 

 speaking of the surface Foraminifera, wrote, " the sea, like the 

 snow-cloud, with its flakes in a calm, is always letting fall upon 

 its bed showers of microscopic shells."* 



It might be supposed that these shells and other surface 

 animals would consume so long a time in dropping to the 

 bottom in great depths that their soft tissues would be decom- 

 posed, and they would have ceased to be serviceable as food by 

 the time they reached the ocean bed. Such is, however, not the 

 case, partly because the salt water of the sea exercises a strongly 

 preservative effect on animal tissues, partly because the time 

 required for sinking is in reality not very great. 



In order to test the matter for myself I made the following 

 experiment. I took a dead Salpa, of about 2 inches in length, 

 and placed it in a glass cylinder full of water, and 3 inches in 

 diameter. I allowed the Salpa to fall from the surface of the 

 water in the cylinder to the bottom a number of times and noted 

 carefully the time which it took to traverse this distance, which 

 was about 8 inches. I found that on an average it took 20 

 seconds to fall the 8 inches. This gives at the same rate, with- 

 out allowance for acceleration, a distance of a fathom to be tra- 

 versed in three minutes, or 2,000 fathoms in four days four hours. 



I allowed the Salpa to remain in the sea water in the 

 cylinder for a long time. It was still not greatly decomposed 

 after having remained in the same water for a month, whilst 

 the ship was in the tropics ; the nucleus was after this interval 

 still undestroyed. The dead animal might have thus sunk to 

 the bottom in the greatest depths almost six times over with- 

 out having become so much decomposed as to be unserviceable 

 for food to deep-sea animals. 



We obtained by our dredgings several interesting proofs of the 

 feeding of deep-sea animals on debris derived from neighbouring 

 shores. Thus, off the coast of New South Wales we dredged from 



* M. F. Maury, LL.D., "The Physical Geography of the Sea," 15th 

 Ed., p. 322. London, Sampson Low and Marston, 1874. 



