Gemmation appears to occur in Acanthocystis and Clathridina. A. viridis has been seen with a small uni-nucleate sphere, possessed of a contractile vacuole and one or two chlorophyl bodies lying beneath an elevation of the shell. It escaped, became uni- or bi-flagellate, and then Actinophrys-like (Korotnefif). In A. aculeata round or oval nucleated bodies were observed by Hertwig lying in a depression of the parent's body. They escaped through the shell, and in some instances developed two flagella. A rounded and nearly detached segment of the shell containing a non-nucleated (?) sphere of protoplasm was seen in one specimen. The sphere was resolved into six portions, which were set free one by one and became Actinophrys-\ike, The parent produced a second similar structure. Clathridina is said to become vacuolate, and to develope small knobs on the surface which are detached, become Actinophrys-like, form a peduncle and shell2.
1Leidy has described a Raphidiophrys socialis, the individuals of which are simply entangled by their pseudopodia. Gruberhas found in Actinophrys sol that fusion may occur (I) between two small non-nucleated specimens, (2) between a non-nucleated individual and a nucleated, a specimen of the latter absorbing three of the former, but repelling a fourth, and (3) between two nucleated individuals, repulsion however often occurring. He concludes that the process indicates an augmentation of substance, and not a reproductive phenomenon. The non-nucleated individuals referred to are of unknown origin. They have pseudopodia, an ecto- and endo-sarc, non-contractile vacuoles, and sometimes a contractile vacuole; they move and feed. See lit. p. 873, infra.
2Biflagellate zoospores have been seen given off from a green Actinophrys sol; they sometimes contained a chlorophyl granule (Archer, Q. J. M. x. pp. 306-7; xvi. p. 300). Biflagellate spores have been also observed in the same Heliozoon by R. Hertwig (J. Z. xi. p. 340). Greeff saw a multitude of minute Amoebae creep out of a dead Actinosphaerium and change into flagellate districts. A few are exclusively marine, e. g. Actinolophus. Some are common to both media, e. g. Actinophrys, Heterophrys, Acanthocystis. The genus Orbulinella inhabits salt-pools near Klausenberg in Transylvania.
Encystation occurs, in some instances preceding reproduction, in others of unascertained significance. Actinophrys secretes a gelatinous capsule and retracts the pseudopodia, whilst the vacuoles disappear. The inner part only (?) of the protoplasm divides, and each part forms a double cyst; the outer cyst ruptures, the inner with its contents escapes; the contained mass shows a separation of ecto- and endo-sarc, developes a contractile vacuole and pseudopodia, by which the inner cyst is pierced and dissolved (Cienkowski). Or there is a double cyst, within which the animal may or may not divide; a contractile vacuole persists; both cysts are ruptured to give exit to the contents (Lieberkuhn). In Actinosphaerium the radiant pseudopodia are withdrawn, but branched pseudopodia of varying length are thrown out and the animal creeps about for twenty-four hours. A thick gelatinous coat is then formed, the vacuoles disappear, and the nuclei are said to diminish in number (Schulze, Brandt). The protoplasm next divides into 2-35 portions successively (Schulze, Greeff), or simultaneously (Brandt). Each portion is uni-nucleate, or else becomes so (Schneider), and surrounds itself with a siliceous cyst (Schulze). Or they fuse in pairs so as to reduce the number present by one half, with or without an odd member (Greeff); or again, each part forms a thin membranous cyst, divides into two within it, the two parts subsequently fusing and the cyst disappearing (Brandt). Ultimately a siliceous cyst is formed, continuous or of small pieces (Schneider, Brandt), single, or double (Greeff). The young Actinosphaerium escapes in spring, and is uni-nucleate (Schulze) or multi-nucleate (Schneider, Brandt). When Clathrulina encysts it contracts and developes a spinose siliceous envelope; or it divides previously into two or more portions, each of which then forms a separate and similar envelope.
Actinolophus surrounds itself with a gelatinous coat, on the outer surface of which appears a layer of loosely arranged hexagonal siliceous plates. The pseudopodia are retracted, their axial filaments and central granule disappear, whilst the nucleus divides into two. Further changes have not been witnessed. The contraction of the body into a small sphere, the formation of a thin or thick envelope round it, or of a siliceous cyst (Pompholyxophrys, Acanthocystis turfacea s. viridis), has been recorded in several genera.
The Heliozoa are a class widely distributed over the world. The greater number of genera are freshwater and are found especially in peat spores (SB. Niederrhein. Ges. in Bonn, 1871). Foulke states that a Clathrulina became rilled with green particles actively motile, which were expelled, a number together, in a thin sac; by the bursting of the latter they were set free, but were not traced further (A. N. H. (5), xiv. p. 269). It is probable that these and similar observations refer to parasitic organisms. Brandt indeed has confirmed Greeff (supra), but has seen the organisms in large numbers within the food vacuoles, and their multiplication when expelled from the body. He refers them to a parasite akin to the fungus Pythium (Monatsb. k. Acad. Berlin, 1881, p. 399). Foulke has described the ejectment of globules from two fused Actinosphaeria which eventually developed into the parent form (A. N. H. (5), xii. p. 206).
Ciliophrys infusionum and Dimorpha mutans are sometimes regarded as Heliozoans. Butschli classes them among the Flagellate Rhizomastigina (p. 841). The same authority includes among Heliozoa, Vampyrella, Nudearia, Monobia, and Myxastrum, which are here retained among Proteomyxa (p. 915 et seqq.) where they are placed by Ray Lankester.