PHYLUM CCELENTERATA 



Class : Hydrozoa 

 HYDRA 



This small animal is of general although sporadic distribu- 

 tion throughout the country. It frequents ponds and streams 

 abounding in plant life and is best obtained by collecting water 

 together with water plants, sticks, and other objects from several 

 such places, and allowing it to stand in glass jars. The polyps 

 will, if present, be seen, after an interval of some time, attached 

 to the stems or leaves of the plants or to the sides of the jar. 

 They may be kept indefinitely in aquaria of this sort and will 

 usually multiply rapidly. Three species of Hydra are common in 

 this country : the brown or reddish hydra {Hydra oli gactis) , y^hich. 

 has tentacles much longer than the body, the green hydra (Hydra 

 viridissima) , and the gray hydra {Hydra vulgaris), both of the 

 latter species having relatively short tentacles. 



Hydra is a slender, tubular animal from one eighth to one 

 half an inch in length ; it attaches itself by one end to some sta^ 

 tionary object and projects pendant in the water ; at the other 

 end is the mouth, surrounded by from four to eleven long, thread- 

 like tentacles. It does not attach itself permanently to one place, 

 but can crawl about or swim slowly through the water. Its food 

 consists largely of small crustaceans which it kills or paralyzes 

 with the peculiar stinging organs called nettle cells, located 

 principally in the tentacles. 



Study the animals first, if possible, without disturbing them 

 and with the aid of a hand lens. Note the extreme contractility 

 of the body. Look for individuals with distended bodies. These 

 have just swallowed prey. Look for budding individuals ; bud- 

 ding is one method of reproduction. Observe the color of the 



animal. 



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