OCEAN ANIMALS: SPONGES, SEA-ANEMONES, ETC. 125 



alive should, if possible, examine some preserved speci- 

 mens in connection with the following brief account. The 

 hard parts of the sponges, sea-urchins, starfishes, and 

 corals, and various sea-shells, are common curiosities, and 

 may be found in somebody's house in almost every town. 

 Sponges. — A bath or slate sponge is simply the skel- 

 eton, or part of it, of a sponge animal. In life all of this 

 skeleton is inclosed or covered by a soft, tough mass of 

 sponge flesh. Sponges are fixed, except when very 

 young, when they swim freely about. They are found at 

 all depths and in all seas, growing especially abundantly 



Fig. 86. — A simple sponge, Grantia; at right a longitudinal section to 

 show the simple body-cavity. (One-half natural size; after Jordan and 

 Kellogg.) 



in the Atlantic Ocean and the Mediterranean. A very 

 few kinds live in fresh water, being found in lakes, rivers, 

 and canals, in all parts of the world. The shape of the 

 simplest sponges is that of a small vase, or nearly cylindri- 

 cal cup, attached at its base, and having at the free end a 

 large opening (fig. 86). But most sponges are very unsym- 

 metrical and grow more like a low, compact, bushy plant 

 than like the animals we are familiar with. The smallest 

 sponges are only i mm. (1/25 in.) high, while the largest 



