12 C. F. ROUSSELET ON PRESERVING ROTATORIA. 



and transfer the prepared Rotifers with a pipette into the cell, 

 then place another drop on the slip by the side of the cell, about 

 half an inch to the left, lower your clean cover glass on to this 

 last drop, which will present no difficulty, then with a needle 

 push the cover glass slowly, and by little jerks, over the cell, 

 stopping short for a moment if the Rotifers show a tendency 

 to move to the edge of the cell. But before covering the cell 

 examine it under the dissecting microscope, and remove every 

 fibre and every particle of foreign matter, however small, with 

 a mounted bristle. The superabundant fluid is then removed 

 with blotting paper until none is left round the cover ; the cover 

 must not, however, stick too fast, and you must be able to move 

 it with a needle, otherwise the cement will be forced in at the 

 sides by atmospheric pressure. When ready the cover glass is 

 sealed down by tipping some Miller's caoutchouc cement* all 

 round the edge with a fine sable brush. The cement must not 

 be liquid, but thickened by exposure to the consistency of a very 

 soft jelly. The edge of the cover-glass must be carefully looked 

 over under the lens to see that the cement covers it everywhere, 

 and that no air bubble has been left at the edge. Cover-glasses 

 have frequently small cracks runninginward some little distance; 

 these must be carefully covered with cement to their ends, 

 otherwise the fluid will slowly evaporate through these cracks, 

 and in time an air bubble will appear in the mount When 

 the cement is dry, that is next day, the slide can be finished 

 with a ring of asphalt, or any other ornamental cement. 



In conclusion, I wish to say that my object in this method of 

 preserving Rotifers is not to bring out any particular organs or 

 structures, but to preserve the animal as a whole, white and 

 transparent, and as life-like as possible, and suitable for identi- 

 fication and study at any time. The process as now explained 

 certainly does this for the great majority of species, and the 

 delicate organs even, such as the very fine flagella attached 

 to the vibratile tags in Asplanchna priodonta, are perfectly pre- 

 served, and can be seen more distinctly than in the living 

 animal. The red eyes and green food particles in the stomach 



* Miller's caoutchouc cement is very good, and the best I know for scaling 

 all kinds of fluid mounts, except, of course, alcohol. Its composition is kept 

 a profound Becret by the inventor, but it probably consists of a mixture of 

 shellac (buttonlac) dissolved in strong alcohol (or possibly Venetian tur- 

 pentine) and caoutchouc dissolved in chloroform. The diluting fluid is a 

 mixture of e<pial parts of chloroform and strong or absolute alcohol. 



