THE FRESH-WATER POLYP {Hydra 



Hydra is a small fresh-water animal, occurring in lochs, ponds, ditches, 

 etc. If a glass jar is filled with some water and weeds collected from a pond 

 and allowed to stand for a while undisturbed, then there may be seen little 

 whitish or green bodies, from 2 to 6 mm. in length, adhering to the weeds 



"Enteric cavity 



- -Ovum 

 - Ovary 



Fig. 10.— a. Hyd/ra, viridis x 10 ; B. Longitudinal Section of Hydra, viridis. 

 After Parker and Haswell. 



or to the sides of the jar. Cut off a piece of weed to which a Hydra is adher- 

 ing, or remove one with a pipette or a dipping tube, and place it on a slide in 

 a drop of water. Cover with a supported cover-slip, and examine under the 

 low power of the microscope. 



A. General Form and External Features. 



Htjdra, when fully extended, has a long and slender thread-like appear- 

 ance. Its tubular body is attached at one end by a flattened basal disc. 



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