26 
REVIEWS. 
shell of flint, which almost always presents upon its surface the most 
exquisite sculpture, varying from species to species, and in its delicacy and 
beauty exhausting our conceptions of decorative form. 
These wonderful little bodies are sometimes solitary; but they are often 
found associated into companies, in which the individual members are 
united to one another, so as to form curious zig-zag chains, or flat ribbons, 
or radiating fans, or elegant little trees. When exposed to the action of 
strong acid or of fire, the soft, vegetable cell is consumed, and the flinty 
case remains behind entirely unaltered, and retaining all its beautiful 
sculpture; and though thousands of years may have passed away since 
the living vegetable was encased within its walls of flint, this same 
sculpture will be preserved as perfect as if it were only a thing of 
yesterday. 
To become the possessor of the extraordinary productions we have thus 
attempted to describe, you have only to make a careful search in the 
nearest stagnant pool, or running brook, or along the sea-shore at low 
tides ; you will be then almost sure to find multitudes of Diatomacece — 
for such is the name given by naturalists to the bodies now under consi¬ 
deration—forming a brownish-yellow covering, like fine down or velvet, 
on the stems and leaves of various water plants, or on submerged stones, 
or spreading over the mud at the bottom of the water, or floating as a 
a thin film upon the surface. The Diatomacece being thus recognised, you 
are to collect them from the different localities, in small, wide-mouthed 
phials. It is, in most cases, impossible to obtain them at the time of col¬ 
lection free from mud and other extraneous matter ; but, to separate them 
from the various impurities with which they are associated, you have only 
to expose them in water for a few hours to the light of the sun, admitted 
through the window of your room, and then, by that mysterious sympathy 
which exists between light and organized beings, the Diatoms will separate 
from the surrounding impurities, and congregate at the light side of the 
vessel. 
But when once the Diatoms are in your possession, and you have fitted 
them, by separation from extraneous matter, for examination under the 
microscope, an important question at once suggests itself—How are you 
to proceed in the study of them ?—how are you to find out all that is 
already known about the produce of your day’s collection ?—and how are 
you to satisfy yourself that any particular species has been already described, 
or may not be a totally new form which you have been so fortunate as to 
discover ? 
Two years ago this would have been a difficult task for the English natu- 
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