284 



GENERAL ZOOLOGY 



name "bath sponges" are but the skeletons of sponges of 

 this last type. The tissues of the dead sponge are allowed 

 to disintegrate and fall away leaving only the skeleton 

 or framework of fibers as the part desired for market. 



A fresh-water sponge 



Upper portion of figure natural 

 size, lower portion enlarged 



In the living sponge two dif- 

 ferent kinds of openings are 

 usually recognizable. These 

 are the very numerous small 



pores scattered over the surface of the body, and a few larger 

 openings. Each of the larger openings is called an osculum 

 (Lat., "little mouth"), because it was long thought that 

 this opening was the mouth leading into a digestive canal. 

 Examination of a living sponge shows that this is not true. 

 Water bringing minute particles of food" passes in through 

 the small pores and leaves the body of the sponge by way 



