C. F. ROUSSELET ON PRESERVING ROTATORIA. H 



still swimming about at a reduced speed; with a few only it 

 is necessary to wait until the cilia have ceased beating. 



Notommatadce. Those members of this family which are 

 possessed of a slightly stiffened skin can be preserved easily 

 enough, but the very soft, larviform species present greater 

 difficulties, as they wriggle about constantly from one shape 

 into another when under the influence of the narcotic, and it 

 requires patience to kill them well extended. By trying 

 several times one succeeds in getting a few good ones, suffi- 

 cient for a slide ; so I have Notommata aurita with both auricles 

 fully extended. It must here be mentioned that the formalin 

 causes the black or opaque brain sac, which is so characteristic 

 of some species of Notommata, to clear up and disappear. This 

 is a drawback for these particular Rotifers, and I recommend 

 that these species be preserved in the bichloride of mercury and 

 salt solution, which preserves these structures. 



The Philodinadce also offer considerable difficulties on account 

 of their very soft and contractile bodies. I think, however, these 

 difficulties are not insurmountable, but have not yet had many 

 opportunities, having been so much occupied with other species 



I may remark in passing that infusoria can be preserved by 

 the same method. All those infusoria which have not the 

 power of contraction are readily prepared, without narcotizing, 

 by killing and fixing with j °/ osmic acid, washing out im- 

 mediately in water, and preserving in 2| 7 G formalin. The con- 

 tractile infusoria will have to be narcotized in some way, but 

 owing to the absence of a differentiated nervous system this 

 may prove somewhat difficult ; I have not investigated how far 

 this can be done with 2 D / coca'in and the cocai'n-spirit mixture, 

 but both these fluids should be tried. 



A few hints and wrinkles on mounting Rotifers when killed 

 and prepared may prove useful. 



Instead of cement cells I now use hollowed out glass slips, 

 which can be obtained of all sizes from Jin. to fin. in diameter, 

 and proportionately deep. These are always ready, and have 

 the great advantage that the often very minute animals cannot 

 go to the edge, where they cannot be properly seen in a cement 

 cell. Some difficulty may be experienced at first in closing the 

 cell with a cover glass without an air bubble. This will, how- 

 ever, soon be overcome by proceeding as follows : — Place a drop 

 of the 2\ per cent, formalin solution in the cell, just filling it 



