110 e. penard on the collection and preservation of 



Examination. 



It is not my intention to deal here with a thorough examina- 

 tion of rhizopods, but there is one detail to which T believe 

 it useful to draw attention. 



It often happens that a certain animal, found under the 

 cover-glass in the midst of organisms and debris of all kinds, 

 does not lend itself to observation without difficulty : it is half 

 hidden by the detritus, or will soon be hidden altogether. Now, 

 it is essential for a good observation (as, for instance, to examine 

 the nucleus or to make it come out of the animal) that the 

 specimen be isolated and examined in a drop of clean water. 

 I do this in the following way : 



Suppose that the organism, for example a small Difflugia, 

 is under the cover at the place marked by the little cross shown 

 in Fig. 1. I note the exact position : I see, for instance, that 

 a little below and to the left of the Difflugia is an easily visible 

 object, let us say a large diatom. 



I carefully transfer the slide to the dissecting microscope 

 (la loupe montte), where I easily find the diatom again, which, 

 this time, as the object is no longer inverted to the observer's 

 eye, should appear to the right and above the Dijflugia, and, 

 thanks to this point of reference, I am able to discover the 

 latter (Fig. 2). 



At this moment, without losing sight of the Difflugia for 

 an instant, I add to the right edge of the cover a large drop 

 of water (Fig. 2), and then with a needle I get rid of the cover 

 by sliding it to the right (Fig. 3).* 



The little Difflugia is still there, but this time in open water. 

 With the same needle I push it to the left, always enclosed 



and collects almost nothing) ; but as regards rhizopods, there is no cause 

 for anxiety, for these organisms live exclusively on the bottom : in large 

 lakes one never finds them in the open water, except the curious Difflugia 

 hydrostatica, which is sometimes pelagic, and sometimes, perhaps, 

 Cyphoderia ampulla. For the rest, even with a marsh, one must never 

 forget that only the bottom will be generally productive, except where the 

 bottom is clothed with aquatic plants, which rise to the surface, carrying 

 with them the organisms which are borne on their stalks. 



* The addition of this drop of water is only to allow the cover to slide 

 easily by floating on the liquid. Without this precaution it would dis- 

 arrange everything when moved, and the DifHugia would run the risk 

 of being lost. 



