Fig. loo. Diagram of a section of the wall of the sponge Leucandra aspersa, 

 showing the direction of the currents. After Bidder. 



OSQ 



f\^ I \ 





ost 



S^W exhc 





ink c 



Fig. loi. Diagrams of the canal systems of sponges. Partly after Minchin. 

 I, Ascon grade. 2, Sycon grade. 3, Leucon grade. 4, Leucon with small, 

 round flagellated chambers, exh.c. exhalant canal; inh.c. inhalant canal; 

 fix. flagellated chamber; osc. osculum; ost. ostium ;/)ar. paragaster;/)or. pore. 



