THE FRESH-WATER HYDRA 23 



VII. THE FRESH- WATER HYDRA 



Materials. Hydras in glass jars, pipette, watch glasses, hand 

 lens or low-power objective, glass slides and cover glasses, com- 

 pound microscope. 



Directions. (The fresh-water hydra is found nearly everywhere 

 in ponds, ditches, and pools, attached to sticks, leaves, etc. It is 

 often found among duck weed. We have often found the green 

 hydra in ditches among spirogyra. Collect some of these materials 

 and place them in glass jars in a warm room some days before needed. 

 The hydras, if present, will be seen attached to the sides of the jar.) 



A. STUDY OF LIVING HYDRA. Observe them in the jar. 

 Are they free or attached? How do they differ from 

 paramecia in regard to their movements? What is the 

 shape of the body ? What is on the free end of the body ? 

 How many of these tentacles are there? Do they have 

 the power of movement ? Tap the jar and note the effect. 



What is the color of the hydra ? (There are two species, 

 the green hydra and the brown hydra.) Is the free end of 

 the hydra held up or down? If neither, how is it held? 

 Note the gentle swaying of the body and tentacles. When 

 the hydra contracts, what shape does the body assume? 

 Also note the appearance of the tentacles when they contract. 



B. EXTERNAL FEATURES. By means of a pipette or 

 glass tube, remove one of the hydras and place it in water 

 in a watch glass. 



With a hand lens or low objective, note the long, cylin- 

 drical body. Note the tentacles and their number. Note 

 the irregularities or small knobs all over the distal end of 

 the body and the tentacles. Tap the glass and note effect. 



Get one in position to note the mouth between the bases 

 of the tentacles. The attached end of the body is called 



