Page:Encyclopædia Britannica, Ninth Edition, v. 19.djvu/868

Rh 844 PROTOZOA [lIELIOZOA. of the network appear to consist of contractile protoplasm, whilst in the latter they an- described as firm horny threads exuded by the spindle-cells. Neither form has been re-examined since its discovery ; and it is possible that this apparent difference will be removed by further study. . / /, Fro. .VII. Heliozoa. 1. Actinnphryg sol, Ehrh. ; x 800. a. food-particle lying in a large food-vacuole ; b, deep-lying finely granular protoplasm; c, axial filament of a pseudopodiurn extended inwards to the nucleus ; d, the central nucleus ; e, contractile vacuole ; /, superficial much-vacuol ated protoplasm. 2. Clathrulina eleyaim, C ienk. ; x 200. 3. Ileter- opftrj/&quot; manna, H. and L. x CCO. a, nucleus ; b, clearer protoplasm surrounding the nucleus, c, the peculiar felted envelope. 4 Jlaj&amp;gt;fii- diophryg paUida, F. E. Schultze ; x 430. a, food-particle ; b, the nucleus; c, contractile vacuole ; d, central granule in which all the axis-filaments of the pseudopodia meet. The tangentially disposed spicules are seen arranged in masses on the surface. 5. Acanthocygtis tnrfucra, Carter ; &amp;lt; 240. a, probably the central nucleus; b, clear protoplasm around the nucleus ; c, more superficial protoplasm with vacuoles and chlorophyll corpuscles ; d, coarser siliceous spicules ; c, finer forked siliceous spicules /, finely granular layer of protoplasm. The long pseudopodia reachiii&quot; beyond the spicules are not lettered. C. Bi-flagellate &quot; flagellula&quot; o? Acanthiw/xtit acttleata. a, nucleus. 7. Ditto of Clathrulina fit-gam. 8. Attroditculut rubrr, Oreelf ; x 320. a, red-coloured central sphere (? nucleus) ; b, peripheral homogeneous envelope. CLASS V. HELIOZOA. Haockel, 1866. Characters. Gymnomyxa in which the dominating amreha phase has the form of a spherical body from the surface of which r.idiate numerous isolated filamentous pseudopodia which exhibit very little movement or change of form, except when engaged in the inception of food-particles. The protoplasm of the spherical body is richly vacuolated ; it may exhibit one or more contractile vacuoles and either a single central nucleus or many nuclei (Nuclearia, Actino- sph.Trium). Skeletal products may or may not be present. Flagel- luhe have been observed as the young forms of some species (Acan- thocystis, Clathrulina), but very little has been as yet ascertained as to spore-formation or conjugation in this group, though isolated facts of importance have been observed. Mostly freshwater forms. FIG. VIII. Heliozoa. 1. Actinospkierium Eichhornii, Elir. ; x 200. a, nuclei ; b, deeper protoplasm with smaller vacuoles and numerous nuclei ; c, contractile vacuoles; il, peripheral protoplasm with larger vacuoles. 2. A portion of the same specimen more highly magnified and seen in optical section, a, nuclei ; b, deeper protoplasm (so-called endosarc); d, peripheral protoplasm (so-called ectosarc); e, pseudopodia showing the granular protoplasm streaming over the stiff axial filament;/; food- particle in a food-vacuole. 3, 4. Nuclei of Actinosphaerium in the resting condition. 5-13. Successive stages in the division of a nucleus of Actino-phferium, showing fibrillation, and in 7 and 8 formation of an equatorial plate of chroniatin substance (after Hcrtwig). 14. Cyst-phase of Actinosphierium Kiehhmnii, showing the protoplasm divided into twelve chlamydospores, each of which has a siliceous coat ; a, nucleus of the spore ; &amp;lt;j, gelatinous wall of the cyst ; h, siliceous coat of th&amp;lt; spore.