FOOD-MATTERS IN THE SEA 317 



similar organisms is contained in 1,000 litres of the water. 

 But Prof. G. H. Parker has recently shown that the sponge 

 Spinosella at Bermuda, with about twenty exhalant openings 

 can strain in a day about 1,575 litres, or over 415 gallons 

 of sea-water. 



In addition to the plankton and the nanno -plankton, 

 Professor Prince draws attention to the " Demerson," 

 sinking clouds of dead plankton, which settle on the botton 

 as a colloidal stratum, recalling the now discredited 

 " Bathybius " of pre-" Challenger " times. This demerson is 

 an important source of nutriment for animals at all depths 

 from coast to abyss. Petersen and others have also recog- 

 nized this potential food-matter under the name " detritus." 



The various estimates differ widely. It is probable that 

 different animals differ in their food-requirements according 

 to their habits, and probably localities also vary. It is 

 evident that further data are required, as the calculations 

 of food requirements on our present data must be regarded 

 as of very doubtful value. The food requirements cannot 

 be expected to be proportional to the animal's weight, as 

 exoskeletal and some other structures that add materially 

 to the weight are not active in metabolism. Nor can the 

 surface area be taken as a guide, as surfaces vary greatly 

 in absorbing power. 



Professor B. Moore and several other bio-chemists, in a 

 series of investigations made at the Port Erin Biological 

 Station from 1910 onwards, have shown conclusively that 

 the amount of dissolved organic carbon present in the sea- 

 water of the Irish Sea is almost negligible (lying well below 

 1 mgr. per litre of water), and that Piitter's figures are very 

 incorrect ; his original figure of sixty-five having been brought 

 down by Henze and Raben to six, and then three, and now 

 by Moore to one, which is within the limit of experimental 

 error. Moore has also shown, however, that the amount 

 of plankton normally present and generally distributed 

 throughout the water, avoiding special swarms, is insuffi- 



