PHYLUM PORIFERA 127 



vidual cells can be separated from each other by squeezing some 

 types of sponges through the meshes of a silk cloth. From these 

 living cells, if kept in favorable conditions, a new sponge will 

 reorganize. 



Metabolism 



A sponge obtains food from the water which is continually pass- 

 ing by way of ostia, through the canals and central cavity, and out 

 the osculum. Microorganisms and other particles of organic matter 

 are drawn in with the water. The current is produced by the 

 flagella of the choanocytes and contractility of the walls. It is 

 controlled by the contractility of the cells surrounding the ostia. 

 As the current sweeps the potential food particles into the collar 

 cells they are seized and ingested by pseudopodia, according to 

 some authors. At any rate the food particles are taken into the 

 cytoplasm of certain of the cells. Digestion is intracellular (within 

 cells) in the food vacuoles and the process is much the same as has 

 been described in Protozoa. The digested material is assimilated 

 by diffusion from cell to cell. This may be augmented by the 

 amoeboid wandering cells. Respiration is carried on by diffusion 

 through the general surfaces, and the exchange of gases O2 and 

 CO2, is made with the surrounding water. Catabolism, or the union 

 of oxygen with the fuel substance of the cell to liberate energy, 

 goes on in the cells in some degree as long as they are alive. 

 Excretion is largely by general diffusion through the surfaces, per- 

 haps assisted by the wandering cells. Egestion is probably accom- 

 plished much as it is in Amoeba. 



Reproduction and Life History 



Scypha is able to reproduce both asexually and sexually. The 

 former may be by budding or by the formation of gemmules. Bud- 

 ding involves the branching of new individuals from the external 

 surface of an old one. These new individuals finally become free 

 from the parent. Sometimes a colony is formed by the buds re- 

 maining attached to the parent. Gemmule formation or internal 

 budding is another type of reproduction, found particularly in 

 fresh-water sponges. Groups of cells become separated from the 

 surrounding deep tissue by limiting membranes, which become in- 

 filtrated with siliceous materials. They are usually formed during 

 adverse conditions and can withstand desiccation and other severe 



