00 THE BIOLOGY OF THE ANIMAL 



Draw a portion of the body-wall, showing the arrange- 

 ment of the ceU- layers and the shape and position of 

 the constituent cells. 



Can you detect the presence of eyes or of any organs 

 by which the hydra can perceive light ? Do you find 

 any nerves or muscles ? Brain ? Do you find organs 

 of cmy kind inside the body ? After the foregoing top- 

 ics have been studied, run a drop of dilute acetic acid 

 under the cover-glass. What change takes place in the 

 position of the body and tentacles ? What happens to 

 the nematocysts? Notice the shape and length of the 

 threads. Of what use to the animal can be this be- 

 havior of the nematocysts ? 



From a well-fed community of hydras select an indi- 

 vidual which bears buds, and in addition to the topics 

 studied before, investigate the following : Does the en- 

 teron of the parent extend into the bud ? Do the cell- 

 layers do the same ? Do all of the buds have tentacles ? 

 Up to what point in their development do the buds re- 

 main attached to the parent % To what extent and for 

 how long is the bud dependent upon the parent for food- 

 supply ? Do 3"ou find any buds which are just about to 

 leave the parent? How do you distinguish them ? What 

 appear to be the first steps in the formation of a bud? 



Make sketches showing the manner in which the bud 

 is attached to the parent, buds in various stages of de- 

 velopment, and the relation of the enteron and ceU-lay- 

 ers of the bud to those of the parent. 



Examine mature individuals for the presence of sex- 

 ual glands (testes and ovaries), both of which may be 

 found on the same animal, the former as small, knob- 

 like swellings near the tentacles, the latter as larger 

 spherical swellings farther down on the body. How 

 many testes do you find on one individual? Is the 



