Class 1. =Syngeneticæ.= The individuals are uni- or multicellular, free-swimming or motionless. The cells (which in the multicellular forms are loosely connected together, often only by mucilaginous envelopes) are naked or surrounded by a mucilaginous cell-wall, in which silica is never embedded. They contain one cell-nucleus, one or more pulsating vacuoles, and one to two band- or plate-like chromatophores with a brown or yellow colour, and sometimes a pyrenoid. Reproduction takes place by vegetative division, or asexually by zoospores, akinetes (or aplanospores?). Sexual reproduction is unknown. They are all fresh water forms. To this class may perhaps be assigned the recently arranged and very little known orders of _Calcocytaceæ_, _Murracytaceæ_, _Xanthellaceæ_, and _Dictyochaceæ_, which partly occur in the free condition in the sea, in the so-called “Plankton,” and partly symbiotic in various lower marine animals. The _Syngeneticæ_ are closely related to certain forms in the animal kingdom, as the Flagellatæ. Order 1. =Chrysomonadinaceæ.= Individuals, uni- or multicellular, swimming in free condition, naked or surrounded by a mucilaginous covering. The cells are generally oval or elongated, with 2 (rarely only 1) cilia, almost of the same length, and generally with a red “eye-spot” at their base, and with 2 (rarely 1 only) band-shaped chromatophores. Reproduction by the longitudinal division of the individual cells either during the swarming, or during a resting stage; in the multicellular forms also by the liberation of one or more cells, which in the latter case are connected together. A. Unicellular: _Chromulina_, _Cryptoglena_, _Microglena_, _Nephroselmis_. B. Multicellular: _Uroglena_, _Syncrypta_ (Fig. 11), _Synura_. [Illustration: FIG. 11.--_Syncrypta volvox_: the multicellular individual is surrounded by a mucilaginous granular envelope.] Among the unicellular Chrysomonadinaceæ are probably classed some forms which are only stages in the development of the multicellular, or of other _Syngeneticæ_. Order 2. =Chrysopyxaceæ= are unicellular, and differ mainly from the preceding in being attached either on a slime-thread (_Stylochrysalis_), or enclosed in an envelope (_Chrysopyxis_, Fig. 12). They have two cilia, and multiply by longitudinal (_Chrysopyxis_) or transverse division, and the swarming of one of the daughter-individuals (zoospore). Division may also take place in a motionless stage (_palmella-stage_). [Illustration: FIG. 12.--_Chrsopyxis bipes_: _m_ envelope, _Ec_ chromatophore, _cv_ contractile vacuole.]