Make a drawing of Paramecinm, showing mouth, oral groove and 

 food vacunles and indicate the path of circulation of the food 

 vacuoles by means of arrows. ( Watch carefully for defaeca- 

 tion ; if observed, indicate in your figure where it occurs. ) 



c. Digestion. Feed the animals on green alga cells. ( )l>serve 

 the changes in color in the food vacuoles after they have beem some 

 time in the body. They become yellowish in place of bright 

 green. The difference in color among the different food vacuoK> 

 is commonly easily seen. 



Stain some of the living Paramecia with neutral red, in the follow- 

 ing way. Make a i/iOOO f / f solution of the neutral red. To a small 

 quantity of this add twice this quantity of culture \vater containing 

 many Paramecia, and allow to stand for ten minutes or more. The 

 animals will now be found to be partly stained red. Since this sub- 

 stance stains only structures having an acid reaction, the staining 

 gives an opportunity to determine the nature of some of the chemical 

 processes in development. It will be found that some of the food 

 vacuoles are strongly stained, indicating the presence in them cf an 

 acid. Others will be found colorless, while others are of a palt- 

 yellowish tinge. The latter are those in which digestion is about 

 finished, and the acid, together with the nutritious parts of the food, 

 have been absorbed, and the remaining material has taken an alkaline 

 reaction (to which the yellow color is due). Such a mass is usually 

 found in the posterior part of the body, about half way between 

 the mouth and the posterior end. It consists of waste matter ready 

 for discharge, the discharge taking place at about this point. 



Note the red stained zymogen granules about the vacuoles. These 

 are thought to be the substances giving rise to the ferments of 

 digestion. 



The reaction of the vacuoles can also be followed by feeding on 

 finely divided litmus particles. Try this experiment as a check on 

 the above. 



d. Dcfaecation. Observe this in Paramecia that have been fed 

 with India ink. With a little patience in watching it is usually easily 

 seen in such cases. Represent the place where it occurs on your 

 figure. 



e. Excretion takes place by means of the two contractile vacu- 

 oles. Observe the method by which these are filled ; draw two or 

 three stages in the process, showing the canals, etc. ( )bserve the 

 discharge of the vacuoles in the following way. Place the Paramecia 

 in a thick solution of India ink, so that they appear white against 



