C. F. ROUSSELET ON PRESERVING ROTATORIA. 



9 



animal will have recovered from the first shock, and you can 

 add one more drop of the cocain- spirit mixture, and so on? 

 one drop every three minutes, until five drops have been added ; 

 wait then ten minutes longer, that is 25 to 30 minutes (not 

 more) from the beginning of the process, and Stephanoceros will 

 be ready to be killed with one good drop of J per cent, osmic 

 acid, which is to be placed right on the animal, not run in at 

 the side of the cell. The animal may contract into various 

 shapes during the process, but at the end of the 25 minutes 

 will generally be found fully extended. It is well to place 

 your watch on the table and follow these directions some- 

 what closely. After half-a-minute, wash out the osmic 

 acid, which must be done very carefully, and mount on the 

 same slip in bichloride of mercury and salt solution. It is not 

 advisable to mount more than one Stephanoceros on a slide, or, at 

 least, only one small piece of weed, to which, of course, several 

 animals may be attached. 



It must here be stated that the gelatinous cases of Stephano- 

 ceros, the Floscules, and also of Melicerta tubicolaria seem to be 

 about the only structures which are not well preserved by the 

 formalin ; these cases seem to swell out in length, not in width, 

 squeezing the animals in the central opening. I had some very 

 well prepared Melicerta tubicolaria, the tubes of which have 

 grown to nearly three times their original lengths, showing the 

 heads of the uncontracted animals about the centre. Unless 

 the gelatinous cases are first removed, it will be better to pre- 

 serve and mount these Rotifers in dilute Flemming's fluid with- 

 out osmic acid, or in bichloride of mercury and salt solution.* 



Melicerta ringens is easier to prepare, but requires patience ; 

 little of the narcotizing fluid must be added at first, and the 

 creature watched until the cilia move very slowly, then is the 

 time for killing with a drop of osmic acid. 



Limnias presents no difficulty. After the first dose more and 

 more cocain mixture can be added rather quickly, and the 

 animals may be killed fully extended while the cilia are still in 

 motion. 



GonocMlus volvox must be narcotized very quickly. The first 

 good dose of cocain-alcohol sends the colonies spinning round 



* I recommend that this solution be made as follows, as least likely to 

 produce crystals :— Equal parts of bichloride of mercury, ^ per cent. 

 solution, and common salt, \ per cent, solution. 



