THE HYDRA. 



Phylum III, CCELENTERATA; class i, HYDROZOA; order i, 



LEPTOLIN.E. 



HABITAT. The fresh-water Hydra is very generally distributed 

 throughout the country, but is likely to be absent in some particular 

 locality or spot while abundant in others near by. It is found in ponds 

 and sluggish streams, attached to weeds, sticks, or leaves. There are 

 two common species, one brownish in color, the other green. 



APPEARANCE. This little animal is not at all conspicuous. On 

 the contrary, one must look carefully to distinguish it in a glass jar 

 containing sticks or plant life from a pond. It is tubular in shape, 

 about as thick as a pin, and from one-eighth to one-half an inch in 

 length. One end will usually be attached to the sides of the aquarium 

 or to the water plants, the other swings free and is surrounded by 

 what appears to be a fringe of thread-like organs. 



Technical Note. Specimens of Hydra may be obtained for class use by 

 collecting, from three or four localities, water containing sticks, 

 leaves, or plants. Place this in glass jars and stand the latter in a 

 light place. The polyps will usually do well in such situations and 

 may be kept indefinitely in the aquaria. Transfer specimens to a 

 watch glass and study with a low power of the microscope or with a 

 hand lens. If the polyp is attached to some small object it should be 

 transferred without detaching from the latter. 



MOVEMENTS. Were all the Hydras hi the jar attached? Look 

 for some swimming slowly about or crawling with a looping motion 

 over the surface of the glass or plants. Evidently the attachment is 

 only temporary, the animals being able to release their hold and seek 

 new feeding grounds at will. Note the movements of contraction and 

 extension in the attached specimens. At one moment the polyp may 



