HYDRA 



(Materials: — Phylum Coelenterata, Class Hydrozoa, Or- 

 der Hydraria. 



1. Living Hydra. A living specimen will be given you in 

 a watch glass with a small amount of water. Examine with dis- 

 secting lens while still in the watch glass, using care in handling 

 the specimen to prevent injuring it. Note that the animal is 

 composed of a more or less cylindrical hody which near one end 

 bears a ring of tentacles. At its opposite extremity the body is 

 slightly modified as a foot by means of which it becomes attached. 



II. General Study. 1. Body, size and form. Does the 

 form change. 



2. The foot. See if any debris or foreign material is at- 

 tached to the foot. See demonstration of longitudinal section 

 through foot. (Glandular cells usually stain much darker than 

 other cells.) Examine specimens clinging to the sides of an 

 aquarium or bottle. How do you infer that attachment is 

 eifected ? 



3. The tentacles. How many? Where situated? Change 

 of form? 



4. You have observed that the tentacles are located a 

 short distance back of the extreme tip of the body. The cone- 

 shaped tip of the body which extends anteriorly beyond the bases 

 of the tentacles is termed the hypostome. The mouth is located 

 at the tip or apex of the hypostome. 



5. If micro-crustacea are available, add a drop of water 

 containing a few of them to the watch glass containing a living 

 Hydra. Under the hand lens, watch the tentacles capture a 

 crustacean and bring it into the mouth of the Hydra. 



6. Draw the Hydra when the body is well extended and 

 also when contracted. The extended drawing should be at least 



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