CLASSIFICATION. 
The simplest beings which are recognised as belonging to the Animal Kingdom, that 
is to say, all below the Ccelenterata in point of organisation, are by general consent placed 
together to form the Sub-kingdom Protozoa. They possess one character in common, 
namely, that the body consists of jelly-like protoplasm or sarcode, which, so far as can be 
ascertained, is either structureless or only specialised in a comparatively rudimentary way. 
In many of the constituent groups, the skeleton or framework of the animal takes 
beautifully symmetrical and often complex forms, whilst the sarcode body retains its 
simplicity, and produces no organ more highly specialised than the nuclei and contractile 
vacuoles, wdricli may or may not be present in the jelly-like mass. 
The Sub-kingdom Protozoa is variously treated by different systematists, but the 
division into three classes, — Monera, Rhizopoda, and Infusoria, commends itself as a good 
working arrangement. Whether the Spongida are more nearly related to the Protozoa 
or the Ccelenterata is a question which need not be considered here. 
Classification of the Rhizopoda. 
The discovery of the true nature of sarcode organisms is due to the French naturalist 
Dujarclin, by whom they were originally described under the collective name Symplecto- 
rneres 1 . In subsequent papers by the same author, preference was given to the term 
Rhizopodes, and this, in its latinised form, has since been almost universally adopted. 
Dujardin’s earlier researches were published in the year 1835, and the number of 
forms then recognised as belonging to the group was exceedingly small ; but before the 
appearance of his memoir on the Natural History of Zoophytes, 2 in 1841, the list had been 
considerably increased ; and, in the classification proposed in that work, the Rhizopoda 
constitute an independent Family of the Infusoria, which, without intermediate group- 
ing, is divided into eight genera, namely : — - 
1. Arcella. 
2. Difflugia. 
3. Irinema. 
4. Euglyplia 
5. Gromia. 
6. Miliola. 
7. Cristellaria. 
8. Vorticialis. 
The author, however, appears to have been well aware that the knowledge of such 
organisms was in its infancy, and he mentions several recent types that he had refrained 
1 Bullet. Soc. Sci. Nat. France, 1835, No. 3, p. 36. 
2 Histoire Naturelle des Zoophytes. — lnfusoires, comprenant la 'physiologie et la classification de ces animaux, 
&c., p. 240, Paris, 1841. 
