Bt ANIMAL LIFE 
sponges. Asin the Protozoa, there are no special organs 
for the performance of special functions. The sponge 
feeds by creating, with its flagella, water currents which 
Fiu. 18.-One of the simple sponges, 
Prophysema primordiale (after 
HarckEL). The body is represented 
as cut in two longitudinally. The 
large cells of the inner layer are the 
egg cells, 
flow in through the many fine 
pores of the body and out from 
the inner body cavity through 
the large opening at the free 
end of the body. These cur- 
rents of water bear fine parti- 
cles of organic matter which 
are taken up by the cells lining 
the pores and body cavity, and 
assimilated. There are no 
special organs of digestion. 
Each cell takes up food and 
digests it. The water cur- 
.rents also bring air to these 
same cells, and thus the sponge 
breathes. Although the 
sponge as a whole can not 
move, does not possess the 
power of locomotion, yet the 
protoplasm of the cells has 
the power of contracting, just 
as with the Protozoa, and the 
pores can be opened or closed 
by this cellular movement. 
Practically, thus, the only 
movements the sponge can 
make are the movements made 
by the individual cells. 
Reproduction is accom- 
plished by a process of divi- 
sion, or by a process of conjugation and subsequent division. 
In its simplest way multiplication takes place by a group 
of cells separating from the body of the parent sponge, 
