BRITISH 

 FRESHWATER RHIZOPODA. 



INTRODUCTION. 



THE 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 

 \\ .. 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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