_Protozoa performing most of their life-processes by pseudopodia; nucleus frequently giving off fragments (chromidia) which may play a part in nuclear reconstitution on division; sometimes with brood-cells, which may be at first flagellate; but never reproducing in the flagellate state.[64]_ 1. RHIZOPODA _Sarcodina of simple form, whose pseudopodia never coalesce into networks (1),[65] nor contain an axial filament (2), which commonly multiply by binary fission (3), though a brood-formation may occur; which may temporarily aggregate, or undergo temporary or permanent plastogamic union, but never to form large plasmodia or complex fructifications as a prelude to spore-formation (4); test when present gelatinous, chitinous, sandy, or siliceous, simple and 1-chambered (5)._ CLASSIFICATION.[66] I. Ectoplasm distinct, clear; pseudopodia blunt or tapering, but not branching at the apex LOBOSA _Amoeba_, Auctt.; _Pelomyxa_, Greeff; _Trichosphaerium_, A. Schneid.; _Dinamoeba_, Leidy; _Amphizonella_, Greeff; _Centropyxis_, Stein; _Arcella_, {52}Ehr.; _Difflugia_, Leclercq; _Lecqueureusia_, Schlumberger; _Hyalosphenia_, Stein; _Quadrula_, F. E. Sch.; _Heleopera_, Leidy; _Podostoma_, Cl. and L.; _Arcuothrix_, Hallez. II. Ectoplasm undifferentiated, containing moving granules; pseudopodia branching freely towards the tips FILOSA _Euglypha_, Duj.; _Paulinella_, Lauterb.; _Cyphoderia_, Schlumb.; _Campascus_, Leidy; _Chlamydophrys_, Cienk.; _Gromia_, Duj. = _Hyalopus_, M. Sch. We have defined this group mainly by negative characters, as such are the only means for their differentiation from the remaining Sarcodina; and indeed from Flagellata, since in this group zoospores are sometimes formed which possess flagella. Moreover, indeed, in a few of this group (_Podostoma_, _Arcuothrix_), as in some Heliozoa, the flagellum or flagella may persist or be reproduced side by side with the pseudopodia. The subdivision of the Rhizopoda is again a matter of great difficulty, the characters presented being so mixed up that it is hard to choose: however, the character of the outer layer of the cytoplasm is perhaps the most obvious to select. In LOBOSA there is a clear layer of ectosarc, which appears to be of a greasy nature at its surface film, so that it is not wetted. In the FILOSA, as in most other Sarcodina, this film is absent, and the ectoplasm is not marked off from the endoplasm, and may have a granular surface. Corresponding to this, the pseudopodia of the Lobosa are usually blunt, never branching and fraying out, as it were, at the tip, as in the Filosa; nay, in the normal movements of _Amoeba limax_ (Fig. 1, p. 5) the front of the cell forms one gigantic pseudopodium, which constantly glides forward. Apart from this distinction the two groups are parallel in almost every respect.