504 LIFE IN THE DEEP SEA. 



The nature of the food of deep-sea animals has been a matter 

 of some consideraljle speculation.* Owing to the lack of sun- 

 light in the depths, there is an entire absence of vegetable life, 

 such as could build up the necessary food of the animals living 

 there, and thus render the cycle of life in those regions self- 

 supporting and complete as it is on land and in the shallow 

 seas. 



Dr. Carpenter tells me he dredged living calcareous algre 

 {Coi-alUnacece) in the Mediterranean Sea at a depth of 150 

 fathoms. As far as I observed, the " Challenger " dredgings 

 did not on any occasion yield algns from so great a depth. The 

 greatest depth from which seaweeds were dredged by us in 

 any quantity was, I believe, 30 fathoms. It is a curious fact 

 that a species of Halophila, one of the Sea Grasses, which are 

 flowering-plants that have become modified to a marine exist- 

 ence, was obtained by us in abundance off Tonga Tabu from 

 so great depth as 18 fathoms. At this depth it was, when we 

 obtained it, in full flower. 



The only plants which extend their range to any great 

 depth are certain lowly organized parasitic Thallophytes, which 

 infest corals and bore for themselves branching tubular cavities 

 in the hard skeletons of their hosts. These parasites have 

 been found by Prof. Martin Duncan in corals which have 

 been dredged from a depth of 1,095 fathoms. t These plants, 

 nourished on the tissues of their hosts, are able to thrive with- 

 out the aid of sunlight, just as do fungi in dark cellars and 

 mines. 



In the absence of plants amongst them, the deep-sea ani- 

 mals have to derive their food entirely from the debris of 

 animals and plants falling to the bottom from the waters 

 above them. This debris is no doubt mainly derived from 

 the surface pelagic flora and fauna, but also to a large extent 

 composed of refuse of 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. i 



* See K. Mobius, "Wo kommt denn die Nahrung von den Tiefsee- 

 thieren her." Z. f. Wiss., Zool. 21. Bd. Heft 2. 



t P. M. Duncan, F.R.S., etc., "On some Thallophj-tes parasitic within 

 recent Madreporaria." Proc. Roy. Soc, 1876, p. 538. 



X M. F. Manry, LL.D., "The Physical Geography of the Sea," I5tk 

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



