HYDRA, 



General Characters. 



Look at hydras in an aquarium. Observe that 



they are found in greatest number on the 



illuminated side. Notice : 



1. Form. 



2. Color. 



3. Movements. 



With a glass tube transfer one or more specimens 

 to a ivatch-glass ; place this on white paper 

 and examine the hydra with a hand -lens. 

 Observe : 



4. The body : cylindrical and varying in length 



and thickness with the degree of extension 

 of the hydra. 

 The parts of the body : 



(a) The basal part, the foot, by which the 



animal adheres to foreign surfaces. 



(b) The conical free end, the hypostome. 



(c) The opening at the summit of the hypo- 



stome, the mouth. 



5. Highly contractile processes of the body-wall 



arranged around the mouth, the tentacles. 

 Count them. 



Note the symmetrical arrangement of the 

 tentacles around the mouth an instance of 



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