CHAPTER III 



SPONGES 



Suggestions. — In man}- parts of the United States, fresh-water 

 sponges may. by careful searching, be found growing on rocks and logs 

 in clear water. They are brown, creamy, or greenish in color, and re- 

 semble more a cushion-like plant than an animal. They have a char- 

 acteristic gritty feel. They soon die after removal to an aquarium. 



A number of common small bath sponges may be bought and kept 

 for use in studying the skeleton of an ocean sponge. These sponges 

 should not have large 

 holes in the bottom ; if 

 so, too much of the 

 sponge has been cut 

 away. A piece of marine 

 sponge preserved in alco- 

 hol or formalin may be 

 used for showing the 

 sponge with its flesh in 

 place. Microscopic slides 

 may be used for showing 

 the spicules. 



The small fresh-water 



sponge (Fig. 21) lacks 

 r , Fig. 21. — Fkesh-water Sponge. 



the more or less vase- 

 like form typical of sponges. It is a rounded mass growing 

 upon a rock or log. As indicated by the arrows, where does 



water enter the sponge? This 

 may be tested by putting color- 

 ing matter in the water near 

 the living sponge. Where does 

 the water come out} (Fig. 22.) 

 Does it pass through ciliated 

 chambers in its course? Is the 



a 



Fig. 22. — Section of fresh-water sponge 

 (enlarged). 



c 17 



