146 



UNIT AND DIVISION OF LABOR 



FIG. 44. Section through sponge wall. Showing 

 fla, flagella, the vibrations of which cause cur- 

 rents of water to flow through the sponge. 



Conclusions. 1. 



What seems to be the 

 . fl a, purpose of the inhal- 

 ent pores? Of the 

 canals ? 



2. What is the 

 course of the water 

 through the canals? 

 Refer to Figure 43. 



3. What causes the 

 water to flow through 

 the canals ? See Fig- 

 ure 44. 



4. How might you 

 compare a sponge with 

 the city of Venice ? 



5. Show that special parts of a sponge have special duties 

 (division of labor). 



2. OTHER SPOXGES (OPTIONAL) 



Material. Small bits of sponge skeletons, slides and cover glasses, 

 portable microscopes, hydrochloric acid, chart. 



Method. Mount bits of the skeleton of grantia and a toilet sponge, 

 and examine with low power. Also test them with acid. 



Observations. 1. Which spicules are needle-like, and which are 

 much branched ? 



2. Which feel the most elastic to the touch ? 



3. Which sort of sponge absorbs water the most readily? 



4. What is the effect when grantia spicules are put in acid ? The 

 toilet sponge ? When each are burned ? 



5. What can you say about the odor of sponges. 



Conclusions. 1. Why is the toilet sponge an article of commerce, 

 rather than the other ? 



2. How does a sponge appear to be protected from fish and other 

 animals ? 



c. The Hydra (Optional) 



Observations. 1. Observe living hydras, either in a small 

 aquarium or in Syracuse watch glasses. 



