Protozoa and Rotifera at Havana, III. 349 



If there are marshes, weedy lakes, or river banks in the 

 neighborhood, many rotifers may be obtained by gathering 

 quantities of the weeds and allowing them to remain for a 

 day or two in a glass jar with water. An examination of the 

 water will then usually reveal the presence of the rotifers. 

 Sometimes it is merely necessary to gather handfuls of the 

 weeds and press out the water, which may be immediately 

 examined. Other forms may be found by searching care- 

 fully the roots of Lemnacece, and the fronds of Utricularia or 

 Ceratophyllum. Many fixed forms may be obtained by care- 

 fully examining the under sides of the leaves of water lilies 

 and pondweed (Potamogeton). If catches are to be made in 

 large bodies of water free from vegetation, a tow-net made of 

 fine bolting-cloth (No. 12) will be indispensable. 



The requisites for the examination of material and the 

 study of rotifers are a compound microscope, several large 

 and small pipettes, watch-glasses, slides and cover-glasses, 

 and several killing and fixing agents. Of course the best 

 results are obtained by studying the rotifers while alive ; but 

 if for any reason this cannot be done the material may be 

 preserved and studied later. If the living subjects under 

 examination are too lively and energetic they may be quieted 

 down by adding to the water, very gradually, a 2% solution 

 of cocaine or chloral hydrate. 



If material is to be preserved, good results may be obtained 

 by killing either in 50% alcohol or picronitric acid*, either 

 of which, after one or two hours should be replaced by 70% 

 alcohol, and this, again, by 80% or 90%, in which the 

 material may be indefinitely preserved. Permanent mounts 

 may be made from material preserved in this way by gradu- 

 ally substituting glycerine for the alcohol, and then mount- 

 ing the objects in glycerine in a cell on a slide. By far the 

 best method of preservation thus far devised is that given by 

 Mr. C. F. Eousselet ('95). He first narcotizes the rotifers 



*The formula for picronitric acid is as follows : 



Water 100 volumes 



Nitric acid (25£ N 2 5 ) 5 



Picric acid as much as will dissolve in mixture. 



Filter before using. 



