CHAPTER II. 
SECOND BRANCH OF ANIMALS. 
SPONGES (Pordfera, pore-bearing). 
General Characteristics.—The sponges were for many 
years considered plants, but now they are known to be 
many-celled animals. In the Ascetfa (Fig. 11), we have 
a vase-shaped cylinder, 7, composed of cells arranged in 
three Iayers. In the second or middle layer is developed 
a network of deli- 
cate objects of lime, 
called spicules (Fig. 
11), that form the 
skeleton, and sup- 
port the’ cellular, jel- 
ly-like mass. The 
walls of the vase are 
everywhere perfo- 
rated with pores, 4, 
through which water 
passes, carrying food. 
The cells of the in- 
ner layer are pro- 
vided with a cilium, Fic. 10,—Spicules of flint-sponges, highly 
or lash, ///, and, magnified. 
taken individually, 
resemble monads. As food floats by, each cilium throws 
the minute bits against its cell; the soft portion is absorbed, 
the harder parts being rejected, and, wafted along by the 
cilia, find egress at the single large opening, O. In this 
2 
