i2 SCIENCE PROGRESS 



But it is possible to calculate how much sea-water does 

 actually pass through these flagellated chambers. The diameter 

 of the osculum is about 6 mm., and the velocity of the 

 exhalent stream of water was estimated by Putter as about 

 5 mm. per second. 1 Thus the volume of water circulated is 

 only about £ litre per hour, assuming that the stream is a 

 constant one, which is not the case, for the osculum is often 

 closed. If, then, the sponge obtains its food-stuffs from the 

 organisms of the plankton, it can obtain, at the very most, 

 •only about 0*0019 mg. of carbon per hour — that is, about 

 s^th part of the carbon it actually excretes ! There does not 

 seem to be any other conclusion than that the mass of food 

 organisms in the planktcn is quite inadequate for the nutrition 

 of the sponge ; and this conclusion would be justified even if 

 we admit that there may be some considerable errors in the 

 estimations of the density of the plankton, and in the estimation 

 of the rate of circulation of the water passing through the 

 canal system of the sponge. 



How, then, do these two animals obtain their food ? There 

 does not appear to be any other conclusion than that they 

 make use of some source of food other than that afforded by 

 the organisms of the plankton, or of the ocean floor. Such 

 sources of food do exist, but before we proceed to consider 

 them it may be pointed out that the processes of alimentation 

 in the sponge and holothurian studied by Putter differ strik- 

 ingly from those characteristic of the warm-blooded animal. 

 In the latter, energy is obtained by the oxidation of certain 

 constituents of the tissue substance, and there is a certain 

 relation between the oxygen absorbed in inspiration and the 

 carbon dioxide excreted. That is, the respiratory quotient, 

 CO2/O2, is a tolerably constant ratio, and indicates that the prin- 

 cipal katabolic process by which the energy of the organism is 

 obtained is an oxidation one. Now so long as we assume definite 

 respiratory functions for such organs as gills, ctenidia, etc., 

 and definite digestive and absorptive function for the alimentary 

 •canal and glands, and assume further that these are the sole 

 functions performed by the organ systems mentioned, it seems 

 natural to suppose that the relation between the inspired oxygen 

 and the excreted carbon dioxide will be similar in value and 

 •constancy to that exhibited by the warm-blooded animal. 



1 Vers;!. Phys. Stoffw. p. 43. 



