FEESH-WATEE POLTP 83 



2. The body proper. — "What is its shape? Does 



the shape change? Is its diameter uniform 

 throughout? Compare the color of this part 

 with that of the disk. Can you discover a cav- 

 ity or enteron inside the body-wall ? Note the 

 mouth at the upper end (hypostome) of the 

 body proper. What is the position of the mouth 

 with regard to the tentacles ? Endeavor to find 

 a specimen lying with the mouth directed tow- 

 ards you, so as to see its shape and size. 



3. The tentacles. — What is their position on the 



body ? How are they arranged ? How many 

 can you find ? Is their number invariable on 

 different specimens ? Are the tentacles of the 

 same size ? Do they ever vary individually or 

 collectively in this respect ? If both the brown 

 and green species of Hydra are available, com- 

 pare the tentacles as to number and variabfiity 

 in both forms. 

 Make drawings illustrating all of the structures stud- 

 ied thus far. 



PHYSIOLOGY 



a. Movements. 



1. Contractility. — What various motions can you 



detect in the body proper ? In the tentacles ? 

 Do either the tentacles or the body change in 

 shape, size, or color as they move ? Are the 

 movements of the various parts at all uniform 

 or rhythmic in character ? 



2. Locomotion. — Examine a jar of hydras, for some 



time if necessary, to see whether or not you 

 can find any of them moving about. If not, 

 with a pen or with a pencil which will mark on 

 glass or with a fine camel's-hair brush put a 



