SPONGES. 
528 
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, flagellated 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 
