STUDY III. CCELENTERATA. Stinging 



Animals. 



Central idea: Division of labor. 



1. HYDRA. 



A. Habitat. 



1. Observe the Hydrse in the aquaria and note their 



position in relation to, — 

 (a) the green water-plants in the aquarium; 

 (6) the sides of the aquarium; 

 (e) the surface of the water ; 

 Id} the light. 



2. Where were the Hydrge obtained ? (Dem.) 



3. How were they collected ? (Dem.) 



4. How are they kept in a flourishing condition in the 



laboratory ? 



B. Shape and Movements. 



1. Show by sketches the various shapes which the 



Hydra assumes during the course of ten minutes. 

 (Examine several specimens in watch-glasses or 

 test-tubes and in the aquaria. Touch gently 

 some of the specimens or disturb them in some 

 manner.) 



2. What is the cause of the changes in shape ? 



3. Observe the great flexibility of the Hydra. 



c 17 



