THE SPONGES 217 



resulted in an attempt to regulate the industry by governmental 

 control. Sponge culture is now carried on successfully in Italy 

 and Florida. Perfect specimens are cut into pieces about one 

 inch square, and " planted " on stakes on clean, rocky bottoms 

 free from cold currents. These grow into marketable size in 

 five or six years. 



Characteristics and Classification. — Sponges are mostly 

 marine animals with bodies that are radially symmetrical but 

 often irregular in shape. The body wall is permeated by many 

 pores, and usually supported by a skeleton of spicules or spongin. 

 Sponges are separated into three classes according to the com- 

 position and shape of their skeletal elements. 



Class 1. Calcarea. — With calcareous spicules, like Grantia. 



Class 2. Hexactinellida. — With silicious spicules, like 

 Venus's Flower Basket. 



Class 3. Demospongi/E. — With silicious spicules or spon- 

 gin, like the Bath Sponge. 



REFERENCES 



Cambridge Natural History, Vol. I. — The Macmillan Co., N. Y. City. 

 Bulletins published by the U. S. Fish Commission. 



