488 PROTOZOA : SPONGIDA. 



IV. RHIZOPODA (including Radiolaria and Foraminifera) ; as Poly- 



cistin, Splicerozoum, Polystomelki, Nummulina, Globiyerina, 

 Cormispira, Gromia, Difflugia, Arcetta, Actinophrys, Amaba, 

 etc. 



V. GREGARINIDA ; as parasitic protozoans. 



VI. MONERA ; as Bathybim, Protomonas, etc. 



SECTION II 



THE SPONGIDA OR SPONGES. 



THE Sponges were formerly regarded by many naturalists 

 as belonging to the vegetable kingdom. They are now 

 regarded as compound animals by all, and by many as 

 being even higher than the Protozoa, having close anal- 

 ogies with the Radiates.* 



The living Sponge is composed of an exceedingly soft, 

 HI my substance, and hard parts which this substance 

 secretes. "Water is admitted through numerous minute 

 pores, which open into a system of branching canals, and 

 these lead into the large pores which we see upon the sur- 

 face, and throuo-h which the water and other bodies are 



O 



discharged (Fig. 740). The water is kept in motion by 

 ciliated cells. Sponges increase by eggs and sperm cells. 



Sponges are common in ponds and lakes, as well as in 

 nearly all parts of the sea ; and their forms are exceed- 

 ino-ly 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. 



As just indicated, Sponges secrete hard parts. They 

 form the well-known "sponge" of commerce. Some 



* See Lieberkiilm, Carter, Clark, Packard (American Naturalist, Vol. IX., 

 No. :2), etc. 



