LABORATORY WORK, XV 359 



1. Touch the tentacles of the Hydra with a needle. What move- 

 ments? 



2. Drop cautiously and at intervals of a few minutes upon the sur- 

 face of the water over the tentacles of the Hydra a drop of water, of 

 susrar solution, of acid. What differences in the movements? 



O 



3. Bring a Daphnia (previously stranded) on the end of a needle 

 to the tentacles of the Hydra. Note the result. With another 

 Hydra, use a bit of plant tissue. 



4. (This and the following experiment must extend through several 

 day*.} Place a Hydra in a watch-glass with a little water, and by 

 means of the needle and a penknife cut it into two or three pieces. 

 Let the pieces expand and draw them. By means of a clean pipette 

 place the pieces in the small Stender dish, in clean water. Draw 

 the pieces again after twenty-four hours, and after a longer period if 

 necessary. 



5. Place in a 4-inch battery jar full of water containing Lemna and 

 Entomostraca two or three large, budding, green Hydras. Cover the 

 jar with the box, placing the slit next to the window. Note at short 

 intervals for two weeks the position and number of Hydras in the jar. 



TOPICS FOR FURTHER STUDY 



1. The habitat and food of Hydra. 2. Other fresh-water or brack- 

 ish-water hydroids (Cordylophora, Limnocodium) and the origin 

 of fresh-water Hydrozoa. 3. Marine hydroids (Obelia, Sertularia, 

 etc.) and their jellyfishes. 4. Sea-anemones and corals. 5. Corals 

 as island builders. 6. Budding and the formation of colonies among 

 animals. 7. Division of labor in colonies. 8. Regeneration in 

 polyps. 



XV. PARAMECIUM 



This exercise requires the use of the compound microscope. 



Tw r o or three weeks before Paramecia are needed, put hay and 

 decaying leaves in stagnant water and keep in a warm room. When 

 the water has become foul, Paramecia have probably appeared. To 

 prevent the Paramecia on the slide from moving too rapidly, it is 

 advisable to put them in a 2.5 % solution of gelatine in water. Study 

 first with the low power, then with the high. To bring out the 



