INTRODUCTION. 33 
rare and curious Ciliophrys infusionwm is that, neces- 
sarily or otherwise, it most frequently occurs in water 
which has been kept two or three weeks in association 
with fragments of pond-vegetation. The occurrence of 
particular species, year by year, in the same ponds, is 
not, however, to be relied upon. 
An aquarium, in which some fine-leaved plants, e. 9. 
Hottoma palustris, Utricularia vulgaris, and Ranwn- 
culus aquatilis, are kept growing without being often 
disturbed, is a valuable adjunct to the study of the 
Rhizopoda. 
PRESERVATION. 
By the employment of dilute nitric acid or sulphuric 
acid it is possible to isolate the Rhizopod nucleus; 
when carmine staining renders a study of that organ 
quite practicable. The process, however, is a delicate 
one. Dr. Eugene Penard has, by the exercise of much 
care and patience, preserved in suitable media numerous 
examples for reference. Where they can be made, 
permanent preparations are no doubt desirable and 
useful, inasmuch as they facilitate a study of the 
nuclear structure under high powers of the microscope, 
but the ordinary student will probably be content to 
make careful drawings from living examples, in different 
aspects and under varying conditions of their existence. 
These, together with descriptive notes, should in all 
cases be preserved. 
The transparent tests of some of the Conchulina, 
when freed from extraneous matter, may be preserved 
in glycerine jelly, and the gritty tests of various species 
of Difflugia can be mounted as opaque objects in the 
same manner as Foraminifera. Beautiful examples, 
obtained by repeated washings of the mud from a 
pond at Chipperfield, Herts, have been obtained by Mr. 
Arthur Harland, showing that this method of treating 
the Difflugiz is feasible and yields good results. 
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