338 THE AMERICAN NATURALIST [Vol. LI V 



The flagella continue to beat for some little time after the 

 animal has come to rest. 



This offers a good opportunity for the observation of 

 the natatory habits, and, as the animals quiet down, for 

 making a closer examination for identification, using 

 higher powers. The smaller the water volume in such a 

 micro-aquarium, the sooner the stupefaction of the con- 

 fined organisms takes place. The forms studied in the 

 micro -aquarium were usually stained intra vitam before 

 their incarceration. 



The stains most frequently used for intra vitam work 

 were methylene blue (not methyl blue) and methyl green. 3 

 With each of these a saturated aqueous solution was pre- 

 pared and diluted to the desired strength. 



The stains which were used for killed specimens were 

 methylene blue (not methyl blue), methyl green, gentian 

 violet, and safranin. 4 



The examination of the imprisoned intra vitam stained 

 animals has the advantage over the killed and stained 

 ones that it shows the position and action of the flagella, 

 and so leads to a more correct idea of how this should be 

 represented in a drawing. Occasionally one meets with 

 the drawing of a form in which the flagellum is repre- 

 sented as thrown into graceful undulations, whereas, in 

 life, it may be only the tip of that organ that is motile. 

 It was found that frequently the killing reagents caused 

 the flagella to assume unnatural attitudes. 



In both the killed and the intra v^am-stained animals 

 the flagella takes the stain least of all, often appearing 

 but very faintly, if at all, colored. In intra vitam stain- 

 ing, care must be taken not to kill the creatures with too 

 much stain in the attempt to make the flagella stain more 

 deeply. 



Killing, in order that examination might be made with 

 the 1.8 mm. objective, using oil, was accomplished by the 

 use of the various well known reagents, such as tannic 



* See formulary of reagents at end of paper. 



