CCELENTERATA. 173 



Devise experiments to test the following questions : 



Is it sensitive to touch? Equally sensitive in all parts 

 of its body and tentacles? Evidences. Has it anything 

 corresponding to a sense of taste? Evidences. Can 

 you get it to take food? Try it with one of the small 

 water fleas often found in aquaria, or with a piece of 

 meat not larger than a small pin-head. Place against 

 the tip of a tentacle. Note every motion of the tentacle 

 and of the body. Can the Hydra swallow? Try simi- 

 larly with a small piece of paper. Compare its behavior in 

 the two cases. Are hydras sensitive to light? 



Classify all the results you have, under the heads: 

 motion, locomotion, nutrition, sensation. Are there 

 any other questions you would like to ask? Can you 

 devise some way to answer them? 



Transfer the living animal to a watch-glass containing 

 a little water and examine with the low power of your 

 microsocpe. Draw carefully the outlines of the animal 

 extended and contracted. What differences can you see 

 between the attached end and the free end? Has the 

 animal any sort of symmetry? What regions and 

 structures of the animal seem to you to need names? Is 

 there any internal cavity? If so, where is it? Are the 

 tentacles solid structures? Evidences. Are there any 

 buds on any of the specimens? If so, draw several in 

 different stages. 



From mounted and stained microtome sections the teacher may 

 at least demonstrate the general arrangement of the ectoderm and 

 entoderm layers in the various parts of the body. 



The nettling cells may be studied, unexploded and exploded, with 

 the high power, by transferring the animal to a slide and covering 

 with a cover-glass. A small drop of dilute acetic acid added to the 

 water will cause many of them to explode. Compare with figures. 



If it is impossible to get living specimens the general structure of 



