Preserving and Mounting Rotifer a 



2} c.c. of the commercial 40 per cent, formaldehyde with 

 87} c.c. of water, and then filtering. 



The above are general directions according to which the 

 great majority of rotifers can be preserved. When under 

 the narcotic, the animals must be watched until it is seen 

 that they can swim but feebly, when, as a rule, they will 

 be ready for killing. If they contract and do not expand 

 again, it is a proof that the narcotic used is too strong, 

 and it must be further diluted. The whole method un- 

 doubtedly requires great care, and is a delicate operation, 

 which must be performed under some kind of dissecting 

 microscope, but by following the directions here given, 

 and with some perseverance, anyone can learn to prepare 

 a large number of species of rotifers. I would advise 

 that a beginning should be made with some such forms- 

 as Brachionus, Anurcea, Synchceta, Asplanchna, Ilydatina, 

 Triarthra, and Potyarthra, which are easy, and, moreover, 

 occur, and can, as a rule, be collected in large numbers. A 

 few genera, however, are exceptionally difficult. These are 

 Stephanoceros, Floscules, Philodina, Rotifera, and Adineta, 

 and it will be better to leave these until considerable ex- 

 perience in dealing with the others has been acquired. 



It will have been noticed that the rotifers must always- 

 remain submerged in a watery fluid, and be transferred in 

 a drop by means of the pipette. Fluids of lesser density 

 than water, such as alcohol, as well as fluids of greater 

 density, such as glycerine, are unsuitable because they set 

 up strong diffusion-currents by osmosis, which cause the 

 animals either to swell or to shrivel up completely. 



Some species of rotifers, such as Triarthra, Polyarihra, 

 Pedalion, Mastigocerca, etc., have an outer surface which is 

 strongly water-repellent, and when these come in contact 

 with the surface film of the fluid even for an instant it is 

 most difficult to submerge them again, and, as a rule, they 

 are lost or spoiled. 



Having then successfully narcotized, killed, and fixed the 

 rotifers fully extended, and finally transferred them into 



