528 



SPONGES. 



from the oscules and branching into the body, and much narrower canals from 

 the groups of pores in the skin. The channels from the pores divide up into 

 minute lacunar spaces, or canaliculi, which finally communicate with the interior 

 of small, spherical, flagellate'd chambers, whose walls are perforated by pores. 

 Each of the chambers is the five-hundredth of an inch in diameter, and groups 



sponges growing on seaweed, a, b, Two of the Desmacidine group ; c, Spongeldia. (Nat. size.) 



of them open each by one wide orifice into a common space, or canaliculus, which 

 joins with others to form canals terminating in large oscular canals. 



The walls of the canals are lined with flat-cells, but in the flagellated 

 chambers the lining cells are more or less cylindrical, and each is provided at its 

 free end with a whip-like appendage, or flagellum ; and, further, the upper margin 

 is expanded into a thin hyaline collar, so that the whip appears to rise from 



