324 C. F. ROUSSELET OX 



necessary to prepare it freshly every tliree or four months by 

 . dissolving the contents of a ^^ gram osmic acid capsule, breaking 

 the sealed glass tube in 10 grams of distilled water. This gives 

 a 1 per cent, solution which can be further diluted as required. 



Having narcotised, fixed and killed the Rotifera, and having 

 passed them through the several changes of formalin solution, 

 the solid watch-glass was transferred to the stage of the 

 Stephenson binocular and the contents examined under a 

 2-inch objective. (In speaking of my Stephenson binocular 

 I ought to mention that it was a Swift model without any 

 condenser or sub-stage illuminating apparatus, but with the 

 body so mounted and arranged that it could be turned aside 

 when not wanted, thus leaving the stage quite free for manipu- 

 lation and the movement of the solid watch-glass and specimens.) 

 The different species could then be sorted out by means of a single 

 bristle (taken out of an old well-worn clothes-brush and mounted 

 in a suitable handle), and isolated in a micro-cell either singly or 

 collectively, the specimens being picked up and transferred by 

 the fine pipette. 



The greatest difficulty I had was with Floscularia and Ste- 

 phanoceros. The latter I at last succeeded in preparing fully 

 extended in the following way : 



I cut off small pieces of weed having one or more animals 

 attached, as a rule six specimens in all ; each of these I trimmed 

 as if ready for mounting. I then placed each of them separ- 

 ately in six different solid watch-glasses, with a pipette full of 

 perfectly clear filtered pond-water to which I added one drop 

 of 1 per cent, solution of Beta-Eucaine, never using or attempt- 

 ing to use more of the narcotic. At first the animals contracted 

 violently and assumed all manner of shapes. After a time, 10 

 to 15 minutes, they became quiet, and then I watched them 

 under the Stephenson binocular until 20 or 30 minutes had 

 elapsed, when I killed and fixed the first one by adding one drop 

 of J- per cent, osmic acid. If this failed I tried the next one five 

 minutes later and so on, until I succeeded in fixing the specimen 



