32 



PORIFERA 



which is a long flagellum ; the circulation of water through 



the sponge is produced by the movements of these flagella. 



A simple form like that just described is found in the 



Fig. 7. Vertical section through Leucosolenia. Highly magnified. 

 (From Minchin.) 1. Sieve-like memhrane covering the osculum ; 

 2. Outer layer ; 3. Collar or flagellated cells (the pointer should have 

 been continued to indicate the cells lining 5) ; 4. Spicules; 5. Gastral 

 cavity. 



