_Anatomy._--Protista Sarcodina, with simple protoplasmic bodies of _granular surface_, emitting processes which branch and _anastomose freely_, either from the whole surface or from one or more elongated processes ("stylopods"); nucleus one or more (not yet demonstrated in some little known simple forms), usually in genetic relation to granules or strands of matter of similar composition, the "chromidia" scattered through the protoplasm; body naked, or provided with a permanent investment (shell or test), membranous, gelatinous, arenaceous (of compacted or cemented granules), calcareous, or very rarely (in deep sea forms) siliceous, sometimes freely perforated, but _never latticed_; opening by one or more permanent apertures ("pylomes") or crevices between compacted sand-granules, often very complex; reproduction by fission (only in simplest naked forms), or by brood formation; in the latter case one mode of brood formation (A) eventuates in amoebiform embryos, the other (B) in flagellate zoospores which are exogamous gametes, pairing but not with those of their own brood; the coupled cell ("zygote") when mature in the shelled species gives rise to a very small primitive test-chamber or "microsphere." The adult microspheric animal gives rise to the amoebiform brood which have a larger primitive test ("megalosphere"); and megalospheric forms appear to reproduce by the A type a series of similar forms before a B brood of gametes is finally borne, to pair and reproduce the microspheric type, which is consequently rare. [Illustration: FIG. 1B.--_Protomyxa aurantiaca_, Haeck. (After Haeckel.) 1, Adult, containing two diatom frustules, and three Tintinnid ciliates, with a large Dinoflagellate just caught by the expanded reticulate pseudopodia. 2, Adult encysted and segmented. 3, Flagellate zoospore just freed from cyst. 4, Zoospore which has passed into the amoeboid state.] [Illustration: FIG. 2.--_Allogromiidea._ 1, _Diplophrys archeri_, Barker. a, Nucleus. b, Contractile vacuoles. c, The yellow oil-like body. Moor pools, Ireland. 2, _Allogromia oviformis_, Duj. a, The numerous nuclei; near these the elongated bodies represent ingested diatoms. Freshwater. Figs. 2, 3, 11, 12 belong to Rhizopoda Filosa, and are included here to show the characteristic _filose_ pseudopodia in contrast with the reticulate spread of the others. 3, _Shepheardella taeniiformis_, Siddall (_Quart. Jour. Micr. Sci._, 1880). Marine. The protoplasm is retracted at both ends into the tubular case. a. Nucleus. 5, _Shepheardella taeniiformis_; with pseudopodia fully expanded. 6-10, Varying appearance of the nucleus as it is carried along in the streaming protoplasm within the tube. 11, _Amphitrema wrightianum_, Archer, showing membranous shell encrusted with foreign particles. Moor pools, Ireland. 12, _Diaphorophodon mobile_, Archer. a. Nucleus. Moor pools, Ireland.]