FRESH-WATER RHIZOPODS. 113 



these organisms — at any rate, those which are furnished with a 

 shell — lend themselves more readily than many others (as, for 

 instance, infusorians or rotifers) to the formation of a collection 

 of types where the specific characters will be clearly distinguished. 

 I should like, therefore, to describe the means I employ. My 

 methods vary according to the case, and I can give three. 



First Method. 



It often happens that there is seen in the midst of algae and 

 various debris which fill the field of the microscope a particular 

 organism, either abnormal, belonging to a rare species, or in 

 course of division, etc., which it is wished to fix at once. In 

 this case I isolate it in the manner shown above, and when it 

 is enclosed in a droplet of pure water on the clean slip, I flood 

 it with a jet of absolute alcohol from a pipette.* 



After a minute or two, during which it is necessary to watch the 

 specimen, which must not be dry for an instant, I add a drop of 

 borax-carmine, then a moment later I add water ; with a needle 

 I push the rhizopod sideways on to a part of the slip which has 

 just been wiped, and I introduce it into a drop of pure water that 

 I have placed there. I clean all the slip (naturally leaving alone 

 the droplet containing the rhizopod), again I flood the drop with 

 absolute alcohol, and again I clean a part of the slip, and on this 

 dry part let fall a drop of oil of cloves ; with a needle I trail a 

 little of the oil like a sort of canal or bridge up to the rhizopod, 

 and lastly I reverse the movement, pushing the rhizopod itself 

 the length of this bridge up to the drop of oil. The slip is 

 cleaned once more, and I push the rhizopod to the centre, leaving 

 round it very little of the oil. I clean again, let fall on the 

 specimen a drop of Canada balsam, cover w ? ith a round cover- 

 glass, and the preparation is finished. 



All this manipulation, which would appear to be long and 

 intricate, has really only lasted ten minutes, often less, but some- 

 times more in difficult cases. It requires a little skill and 

 sustained attention, but offers no special difficulties. 



* Here, as in the two other methods about to be described, this sudden 

 drenching with absolute alcohol is to kill the organism before it has had 

 time to withdraw its pseudopodia. This way is undoubtedly rather primi- 

 tive, and I have no doubt that a naturalist more used to reagents than 

 1 am will be able to get better results ; but it succeeds often enough, and 

 recommends itself by its simplicity. 



