CHAPTER II 

 BRANCH PORIFERA. THE SPONGES 



THE FRESH-WATER SPONGE 



Upon the stones of clear running streams one can 

 commonly see a greenish growth which at first sight is 

 likely to be taken for an aquatic plant. If you rub 

 your fingers upon it, however, you will notice a peculiar 

 spongy feeling, and looking closely will find it very different 

 from a plant. It is rather an example of the Fresh-water 

 Sponge. Its more important features may be determined 

 by means of the following outline : — 



I. — Study and describe the living sponge : its color, 'shape, 



size, surface appearance, and mode of attachment to 

 the object on which it rests. In living specimens or 

 those preserved in formalin, notice with a lens the 

 minute openings in the surface, and see that there are 

 two sets of holes, one larger than the other. Water 

 containing food material enters the internal cavities 

 through the smaller and goes out through the larger 

 openings, the currents being produced by cihated cells 

 lining the passages. Observe also the tiny projecting 

 spicules which form the skeleton of the sponge. 



II. — Feel the sponge with the tips of your fingers, noting 

 the peculiar spongy texture. 



III. — Place a very small piece of the living sponge upon 

 a glass slide ; tease it out with needle points, put on the 

 cover glass, press it down firmly, and examine under 



IS 



