66 THE BIOLOGY OF THE ANIMAL 



first be examined entire, then with a sharp knife or 

 scissors be cut into several sections parallel with the 

 base ; a second specimen should be cut into vertical 

 sections. Small scraps may be torn off the tips of the 

 canals and examined under the low power of the mi- 

 croscope. 



MORPHOLOGY 



a. Shape. — Do you find that all of several specimens 

 have the same general shape ? What is it ? Do 

 you find any noticeable variations from this 1 If 

 so, can you suggest any reasons for such varia- 

 tions? Can you readily detect an upper and a 

 lower side of the sponge body ? How ? Eight 

 and left ? How ? Notice the elevations of the 

 general surface. Have they any relation to the 

 large canals which run through the mass of 

 the sponge skeleton ? 



h. Size. — ^What is the average size of a number of speci- 

 mens ? Do you consider this the average size at- 

 tained by this kind of sponge, or is it merely the 



marhetahle size ? "Why ? 



c. Color. — What is the usual color of a toilet sponge? 



It must be remembered that many sponges are 

 bleached during the process of preparing them 

 for market. Such sponges usually have a bright- 

 yellowish tinge. 



d. Elasticity and porosity. — Squeeze a dry sponge tight- 



ly in the hand. Does the sponge regain its orig- 

 inal size ? Does it show any tendency to do so ? 

 Now put the same sponge into a dish of water 



