RECENT WORK ON MARINE METABOLISM 9 



chambers placed between the two. The internal walls of these 

 chambers are lined with " choanocytes," cells which are provided 

 with prominent collar-like structures, and with long flagella. 

 The lashing of these flagella produces a difference of pressure 

 which results in the establishment of a current of water which 

 enters the canal system of the sponge through a series of pores 

 called ostia, and leaves through other pores called oscula. 

 It is obvious that the substances utilised by the animal as 

 sources of nutritive material must be conveyed to it by this 

 current of water. 



It has usually been assumed that the substances which serve 

 as the sources of food of the sponge are plankton organisms 

 such as diatoms or protozoa suspended in the water circulated 

 through the canal system ; and it has been supposed that the 

 latter are ingested by the choanocytes in much the same manner 

 as a diatom is ingested by a protozoan, such as an Amoeba. 

 Many series of experiments have been made in order to 

 determine the precise nature of these food organisms, and the 

 details of their capture and digestion by the sponge. Usually 

 the animal has been kept in water to which was added suspended 

 particles such as carmine or indigo, and the passage of the latter 

 through the canal system and their further fate has been traced. 

 Most of these experiments seemed to indicate that solid food 

 particles, such as plankton organisms, contained in the cir- 

 culating current of water, form the food of the sponge, and that 

 these are captured by the choanocytes, and absorbed and 

 assimilated in the dermal cells. Altogether the results of such 

 experiments do not seem to have been very successful, that is, 

 from the point of view from which they started — that the sponge 

 fed on solid suspended food organisms. Haeckel came near the 

 truth when he suggested that sponges feed on the insoluble 

 or soluble products of decomposition of other dead organisms ; 

 and Loisel probably came nearer still when he showed that 

 a sponge might live in filtered water to which was added the 

 juices obtained by breaking down the bodies of other sponges. 



Thus the commonly accepted view has been that a sponge 

 finds an adequate food supply in the plankton organisms present 

 in the water current passing through its canal system. Now 

 before we can regard this as established it is necessary to 

 ascertain what are the food requirements of the animal, and 

 whether or not the plankton present in the volume of water 



