NO. 1893. DIRECTIONS FOR COLLECTING ROTIFERS— BEAVCII AMP. 185 



Tliis method is useful not only for rotifers, but most of the accom- 

 panying forms, Oligochaetcs, Plunarians, Entomostraca, and even the 

 smaller Nematodes, are obtained in good condition, as well as the 

 majority of Infusoria, unicellular Algse, and Flagellates. If Protozoa 

 are tlie main object, the narcotization may be dispensed with, as it 

 is mjurious to certain delicate species. Finally, it may be added 

 that the method of Rousselet, that is, narcotization, followed by 

 fixation with dilute osmic acid, and final mounting in weak formalin, 

 is the only known method for the preservation of all the small trans- 

 parent, vacuolate animals — in other words, the great majority of 

 pelagic forms, marme as well as fresh water. It yields results not 

 attainable by any other method. The usual dehydrating and clearing 

 agents ruin nearly all these delicate animals. 



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The United States National Museum will be glad to receive material 

 preserved in this manner and will arrange for its determination. 



