No. 633] FBEE-S W1MMINQ MASTIGOPHORA 



347 



liar characteristic affords a good identification character. 

 During swimming it often turns over and over in the 

 water, at which times the concavo-convex shape of the 

 body becomes appreciable. 



Either individuals of the species N. orbicularis (Fig. 

 16) vary remarkably in size, or there is more than one 

 species, differing, apparently, only in this particular. 

 The form of the body is, however, constant. 



These forms are found, unlike most of the flagellata, 

 most abundantly in fresh waters, particularly in the clear 

 cold waters of springs, that support little plant growth, 

 and they occur usually near the bottom, among the sands 

 and pebbles. 



Their progression through the water is often slow and 

 deliberate, and at such times it seems as though the tip 

 of the flagellum were functioning as an exploratory 

 antenna. 



Formulary op Reagents Used tor Retarding, Killing ang Staining 



1. Retarding Solutions: 



(1) Gelatine Solution. 



Gelatine V± oz. 



Heat, to dissolve the gelatine; then allow to cool to the de- 

 sired viscosity. 



(2) A 1 per cent. aq. sol. of chloretone narcotizes the animals, and 



gave good results with certain forms, though its manipula- 

 tion was a trifle difficult. 



2. Killing Reagents: 



(1) 25 per cent. aq. sol. tannic acid. 



(2) 5 per cent. aq. sol. acetic acid. 



(3) 10 per cent. aq. sol. mercuric chloride. 



(4) 1 per cent. aq. sol. formalin. 



(5) Invert slide with its suspended drop over the neck of a bottle 



containing a 2 per cent. sol. of osmic acid. The fumes kill 

 the animals at once. 



(6) 1 per cent. aq. sol. copper sulphate. This gave the best re- 



sults of anv of the killing reagents. 



3. Stains: 



A. For intra vitam staining. (Make up a quantity of the stain 

 as directed, and then dilute with water to obtain desired 

 depth of color.) 



