HYDRA. 



HYDRA is found in ponds and lakes which contain pond 

 weeds such as, Elodea, Sagittaria, water-lilies, duck weed, 

 and the like, usually being attached to these plants. Speci- 

 mens secured . from such localities and placed in aquaria 

 with aquatic plants will live indefinitely, if supplied with 

 food in the form of small Crustacea or "water-fleas." 



From the aquaria in the laboratory remove hydra with 

 a clean pipette and place in a watch glass with water from 

 the aquarium. Place this dish on the stage of the dissecting 

 microscope and examine the specimens. 



I. Morphology. 



1. Form. Describe the shape and color of the animal. 

 Is the body differentiated into regions as head and base? 

 Is it attached or free? Do the length and breadth remain 

 constant? At the free end of the body is a row of tentacles, 

 how many are there? Is the number the same in all speci- 

 mens? Compare notes with other students to determine 

 this. If both the green and the brown hydra are available 

 compare them in number of tentacles. Are the tentacles 

 smooth and even in contour? Compare the length and the 

 shape of the tentacles when expanded and when contracted. 

 Within the circle of tentacles is a small opening, the mouth, 

 often difficult to see in living animals. 



On the larger, mature, animals will often be found pro- 

 cesses resembling the hydra. These are young hydras, or 



