I 66 ZOOLOGY. 



note the results. How do the other tentacles behave? Place 

 a food-particle directly at the base of the tentacles. How is 

 it swallowed? How long does it take? What becomes of it? 

 How long does it remain in the body? Classify the results 

 which you have attained, under the following heads : motion 

 and locomotion, nutrition, sensation. Devise still other ex- 

 periments to test special points which you desire to know. 



2. General Structure. Transfer a living animal to the 

 slide, covering it with a drop or two of water. Observe with 

 a low power without cover-glass. Draw carefully in outline 

 everything studied. 



Note body regions : 



Foot (attached end). 



Column. 



Tentacles, position, number (examine several specimens). 



Hypostome, surrounded by the tentacles. 



Mouth. 



To what extent do these regions vary in their dimensions 

 during the different stages of contraction of the hydra? 

 Would you say there is any distinct symmetry? Which is the 

 main axis? Is there any indication of an internal (gastro- 

 vascular) cavity? What is its extent? Are the tentacles solid 

 structures? Evidences? Are there any buds in your speci- 

 men? Relation to the parent? To what extent do different 

 parts of the body do different work? 



3. Microscopic Structure. Cover with a cover-glass supported by 

 objects as thick as the animal. Study with a higher power. Verify the 

 points studied above. Follow the gastro-vascular cavity more fully. Is 

 there an aboral opening? 



Body wall. 



Ectoderm, or outer layer of cells. 

 Entoderm, or inner layer of cells. 



Determine the extent of each layer. Are they continued into the ten- 

 tacles? What differences do you find in the thickness of the layers and 

 in the shape and character of the cells of each layer in the various parts 

 of the body? Is there anything between the ectoderm and entoderm? 



In the ectoderm, especially in the knobs on the tentacles, find highly 

 refractive oval bodies, the nettle capsules. Irrigate with a drop of acetic 

 acid, and watch the tentacle all the while. What changes have occurred 



