266 PROTOZOANS. 



wall is pierced by numerous holes which lead into the 

 central cavity, sometimes directly, sometimes by means 

 of winding passages. Water is drawn into these open- 

 ings by means of cilia, and is propelled out through 

 the central cavity to the external opening. The water 

 brings with it minute animals and plants, and bits of 

 dead creatures, which the cells of the Sponge seize and 

 use as food. The Sponge branches so as to form a 

 colony as is seen in the Figures 511 and 512. In the 

 Bath Sponge, these branches are wholly united to each 

 other, so that it seems a shapeless mass. Study, how- 

 ever, will show on the upper surface the large exhalent 

 openings, each corresponding to a member of the 

 Sponge colony. 



The Sponges mostly live in the sea ; a few inhabit 

 the fresh water. They live in shallow water, attached 

 to rocks, etc. Their forms are exceedingly various and 

 often extremely beautiful. Some cover the rocks like 

 a carpet of mosses ; others grow in massive clusters ; 

 others branch like trees and shrubs ; and others still 

 take the form of the most elegant cups, goblets, and 

 vases. They are plentiful in tropical waters about 

 coral reefs. The Sponges of commerce come from the 

 Red Sea, Mediterranean Sea, and West India Islands. 



PROTOZOANS. 



There is a vast number of beings so simple in their 

 structure that naturalists were in doubt, in many cases, 

 whether to call them plants or animals. These are 

 now called Protozoans, a word which means first or 

 simplest animals. A few of the forms are shown 

 in Figures 513-521, — all much enlarged, except Figure 



