34 BRITISH FRESHWATER RHIZOPODA. 



CLASSIFICATION. 



DUJARDIN* made one of the earliest attempts at a 

 classification of the Protozoa, and in his second order 

 of the Infusoria, in which he placed his " Animaux 

 pourviis $ expansions variable" he approached very 

 nearly to the classification of the present day. The 

 three families into which he divided this order 

 Amibiens, Rhizopodes, and Actinophryens corres- 

 pond closely with (1) the Amoebina, (2) the Conchu- 

 lina and Foraminifera, and (3) the Heliozoa. More- 

 over he grouped his three families into two sections, 

 placing the Amibiens and Rhizopodes in one, and the 

 Actinophryens in the other, as we now differentiate 

 the Rhizopoda from the Heliozoa. Later, von Siebold f 

 divided the Protozoa into two classes, the Rhizopoda 

 and the Infusoria, the former including the above 

 three families of Du jar din. This obviously natural 

 primary division served for a time; but advancing 

 knowledge rendered further systematization indis- 

 pensable. 



Four classes or main groups of Protozoa are now 

 generally recognized, namely, the Sarcodina (with the 

 Heliozoa), at the bottom of the scale ; the Mastigo- 

 phora or flagellates ; the Sporozoa ; and the ciliated 

 Infusoria. The inter-relations of the Sarcodina, the 

 only class with which we are now concerned, remain 

 more or less uncertain. Obscurity surrounds the life- 

 history of many forms, rendering a perfect division 

 into genera and species for the present impracticable. 

 Haeckel separated the (supposed) non-nucleated forms 

 from the nucleated, or those in which the existence of 

 a nucleus had been demonstrated, in order to establish 



* ' Hist. Nat. des Zoophytes. Infusoires/ 1841, p. 126. 

 t ' Anatomic der Wirbellosen Thiere/ 1848, p. 3. 



