CH. X] THE CONDITIONS OF LIFE IN THE SEA 231 



many marine animals habit uall}^ feed on this dissolved food-stuff, 

 behaving, to that extent, as saprozoic creatures. Putter investi- 

 gated the metabolism of several marine organisms by estimating 

 the amounts of oxygen, carbon and nitrogen exchanged between 

 the organism and its medium in the unit of time, and per unit 

 of weight. In the case of the sponge, Suberites domuncula he 

 found that an animal of about 60 grammes weight required 

 per hour 92 milligramme cf carbon \ If w^e assume that the 

 sponge obtains its food by eating plankton organisms then we 

 can calculate the volume of water necessary for the provision of 

 this weight of carbon. Assuming that Lohmann's estimates of 

 the density of plankton in the open Mediterranean are true also 

 of the Bay of Naples, Putter found that it would be necessary 

 for the sponge to capture, per hour, all the plankton contained in 

 242 litres of sea water, that is about 4,000 times its own volume ! 



This was obviously impossible, for a rough estimation of the 

 volume of water passing through the osculum of the creature 

 shewed that this could not be more than about 300 cubic centi- 

 metres ; and this volume of water contains only -gfoth part of the 

 carbon required by the sponge. But if the reader will refer to 

 Putter's estimate of the amount of carbon compounds contained 

 in the sea he will find that onl}/ 14'2 c.c. contained as much of 

 this element as the creature demanded. So even if we assume 

 that all the carbon compounds contained in the water are not 

 capable of utilisation as food, and that the absorption coefficient 

 is not a very high one, it is still the case that the water circulated 

 through the cavities of Suberites may have contained enough 

 carbon to supply the hourly requirements of the animal. 



Putter also found that the Holothurian, Cucinnaria gimbei, 

 when kept in an aquarium in filtered sea water, lost weight. Now 

 calculating the loss of carbon due to the loss of body weight he 

 found that the average deficit was 0'015 mgr. per hour for a 

 confinement of six months. But by estimating the actual amount 

 of carbon given off in the metabolism of the animal he found that 

 this was 0'2 mgr. per hour. Thus more than y^^ths of the carbon 

 exchanged between the animal and its medium could only have 



1 "Die Ernahrung des Wassertiere,"' Zeitschr. AUgem. Phys. Bd. vii. 1907, 

 p. 292. 



