156 ELEMENTARY ZOOLOGY. 



life. If the changes come slowly enough, it becomes round, draws 

 in its pseudopodia, forms a protecting wall, and lies quiet until the 

 return of favorable conditions. 



173. Paramecium: A Laboratory Exercise. This animal is 

 especially favorable for laboratory work on account of the ease with 

 which it may be had. Put some grass and some green matter from 

 one or two ponds into a vessel holding half a gallon or more, and 

 allow the materials to decay. Watch the surface of the water and 

 examine under the microscope every few days. 



FIG. 35. FIG. 36. 



FIG. 35. Am&ba in active condition, ec, ectosarc; en, endosarc, containing food 



vacuoles (/) ; n, nucleus; p, pseudopodium ; p.v., pulsating vacuole. 



FIG. 36. Amceba in the encysted or resting stage. 



Questions on Figures 35 and 36. Define the various terms used 

 above in describing the amxba. What changes may the amoeba 

 undergo in its life-history? Why is it thought of as an especially 

 simple cell? 



Activities. Run a little water, into which finely powdered car- 

 mine has been put, under the slide, and watch every activity. 



Describe and figure every kind of movement of which you find them 

 capable. Can you distinguish an anterior from a posterior end? 

 Do you have any reason to believe the paramecia are sensitive to 

 external conditions? What evidences. To what sorts of influences 

 do they respond ? Do they avoid objects ? Do they tend to collect ? 

 Where? What might be the causes of this? Which seems to you 

 most probable? Are they as active at the end of the hour as at 

 the beginning? Can you find the organs of locomotion ? Evidences? 



