BRITISH 
FRESHWATER RHIZOPODA. 
INTRODUCTION. 
Tue Rhizopoda are animals of minute size and 
rudimentary structure, forming, with the Heliozoa 
and Radiolaria, the class Sarcodina of Biitschli. The 
term Rhizopoda—literally meaning “ root-footed ”’— 
now almost universally adopted, was invented by the 
French naturalist Dujardin to distinguish ‘ animals 
provided with variable processes.” 
The Sarcodina, with the Mastigophora (flagellate 
animals), the Sporozoa (a group of endo-parasites), 
and the Infusoria, make up the sub-kingdom of the 
Protozoa, which is represented by some 1600 genera 
and many thousands of species. 
For present purposes we are not concerned with the 
Mastigophora as a group (though, as will be seen later, 
they bear some relationship with the lobose Rhizo- 
pods), nor yet with the Infusoria or the Sporozoa. 
The Radiolaria, also, are excluded from consideration 
by the fact that they are marine; they possess ray-like 
pseudopodia resembling those of the Heliozoa, but differ 
from animals of that sub-class in having a compara- 
tively large “central capsule,’ which is membranous, 
minutely perforated, and marked, usually, by lines 
which divide its surface into polygonal segments. 
The whole of the Protozoa are microscopic crea- 
tures. Their existence was not even suspected until 
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