PORIFERA 



[CH. 



normally in contact, and the outer part of the cell bodies are widely 

 separate, so that here the distinctness of the elements of a cellular 

 tissue is carried to an extreme. From the centre of each collar 

 a long flagelluni arises, and it is by the action of these flagella 



FIG. 37. Vertical section through an oscnlum with sieve-like membrane, and 



a tube of Leucosolenia sp. Highly magnified. From Minchin. 

 1. Sieve-like membrane. 2. Outer layer. 3. Flagellated or collar cells 



(choanocytes). The pointer should have been continued to indicate the 



cells lining 5. 4. Spicules. 5. Internal cavity. 



that water is drawn in through the pores. The sponge lives on 

 the organisms carried in by the current ; these appear to be carried 

 within the collars by the minute whirlpools produced by the 

 individual flagella: they adhere to the collars and are swallowed 

 by them and digested by the cells. It will be seen that the collar is 





