16 SPONGES 
These cifia perform a three fold function; they move in two directions, tor 
ward and back, thus by their movements, they cause an indraught of water : as 
this water, charged with air, bathes them, they gather air from it, and thus 
Fig. 6. 
Section of a small Tube Sponge, life size, which grew from a larger cyt. 
inder, a portion of which is given ato, a. Allen’s eee May 1893, 
