FRESH-WATER RHIZOPODS. 115 



After this I eliminate the carmine by withdrawing portions 

 of the rose-coloured liquid with the pipette several times, re- 

 placing them with clear water. 



In its turn I replace the clear water by alcohol in the same 

 manner, until at last the specimens are in almost absolute 

 alcohol. At this moment I withdraw nearly all the alcohol 

 (taking care, however, that the Diffluyiae are not dry for a single 

 instant) and I replace it by oil of cloves. 



When it is all clear I take in the pipette half a dozen 

 Diffluyiae ; I let the drop fall near one end of the slip, and from 

 this drop, under a lens, I push the Diffluyiae towards the centre 

 of the slip, where I reunite them in a little group. I wipe the 

 slip, and it only remains to cover the Diffluyiae with a drop 

 of Canada balsam.* 



Third Method. 



This method is excellent when, for instance, one wishes to 

 profit by a rich gathering to make a great number of slides at 

 a time. 



In this case I put a small part of the gathering (as far as 

 possible the upper layer of the detritus that was deposited in the 

 jar) into a large test-tube 19 cm. high by 4 cm. wide (7| in. by 

 1| in.) with a flat bottom ; then, when it is quite settled, I 

 carefully decant the liquid, leaving only a very thin layer of 

 water above the deposit. 



After half an hour, when I judge that the animals have spread 

 out their pseudopodia freely, I suddenly turn in to the test-tube a 



* Perhaps the Canada balsam ought to be replaced by some other 

 substance. If it does possess the great advantage of preserving the object 

 indefinitely, it has the inconvenience of drying too slowly, and often after 

 whole years objects in it are displaced. To meet this disadvantage I now 

 use a very thick balsam, almost hard. Putting the bottle which holds the 

 balsam on a thick iron plate, I heat on a very gentle fire until the balsam 

 becomes ver}'- liquid ; then I transfer everything— hot plate and bottle — on 

 to the work-table, where also, quite ready with the specimens centred, are 

 the slides to be covered. The bottle will keep the balsam sufficiently 

 liquid for an hour, at 40° to 50° centigrade, which temperature does not 

 distort the specimens. By this means is gained perhaps a year, or even 

 two, on the time required before the specimens are immovable in the 

 balsam. 



