Page:Encyclopædia Britannica, Ninth Edition, v. 19.djvu/869

Rh RETICULARIA.] PROTOZOA 845 ORDER 1. APHROTHORACA, Hertwig (56). Characters. Heliozoa devoid of a spicular or gelatinous envelope, excepting in some a temporary membranous cyst. Genera. Nuclearia, Cienk. (37) (many nuclei ; many contractile vacuoles ; body not permanently spherical, but amoeboid) ; Actin ophrys, Ehr. (Fig. VII. 1 ; body spherical ; pseudopodia with an axial skeletal filament ; central nucleus ; one large contractile vacuolc ; often forming colonies ; A. sol, the San -animalcule); Actinosphierium, Stein (Fig. VIII. ; spherical body ; pseudopodia with axial filament ; nuclei very numerous ; contractile vacuoles 2 to 14) ; Actinolophus, F. E. Schulze (stalked). OIIDEII 2. CHLAMYDOPHORA, Archer (57). Characters. Heliozoa with a soft jelly-like or felted fibrous envelope. Genera. Heterophrys, Archer (Fig. VII. 3); Sphs&vaetrum, Greeff; Astrodisculus, Greeff(Fig. VII. 8). ORDER 3. CHALAROTHORACA, Hertw. and Lesser (58). Characters. Heliozoa with a loose envelope consisting of isolated siliceous spicules. Genera. Saphidiophrys, Archer (Fig. VII. 4; skeleton in the form of numerous slightly curved spicules placed tangentklly in the superficial protoplasm) ; Pompholyxophrys, Archer; Pinacocystis H. and L. ; Pinaciophora, Greeff ; Acanthocystis, Carter (skeleton in the form of radially disposed siliceous needles ; encysted con dition observed, and flagellula young, Fig. VII. 6) ; Wagn&rella, Meresch. ORDER 4. DESMOTHORACA, Hertw. and Less. Clutracters. Heliozoa with a skeletal envelope in the form of a spherical or nearly spherical shell of silica preforated by numerous large holes. Genera. Orbulinclla, Entz (without a stalk) ; Clathrulina, Cienk. (with a stalk, Fig. VII. 2). Farther remarks on the Heliozoa. The Sun-animalcules, Actino- phrys and Actinosphaerium, were the only known members of this group when Carter discovered in lSb 3 Acanthocystis. Our further knowledge of them is chiefly due to Archer of Dublin, who dis covered the most important forms, and figured them in the Quart. Jour. Micr. Sci. in 1867. Some of the Proteomyxa (e.g., Vampyrella) exhibit &quot;heliozoon- like&quot; or &quot; actinophryd &quot; forms, but are separated from the true Heliozoa by the fact that their radiant pseudopodia are not main tained for long in the stiff isolated condition characteristic of this group. It is questionable whether Nuclearia should not be relegated to the Proteomyxa on account of the mobility of its body, which in all other Heliozoa has a constant spherical form. Actinophrys sol is often seen to form groups or colonies (by fission), and so also is Raphidiophrys. It is probable from the little that is known that reproduction takes place not only by simple fission but by multiple fission, producing flagellate spores which may or may not be preceded by encystment. Only Clath rulina, Acanthocystis, Actinosphaerium, and Actinophrys have been observed in the encysted state, and only the first two have been credited with the production of flagellated young. The two latter genera form covered spores within their cysts, those of Actino- spluerium being remarkable for their siliceous coats (Fig. VIII. 14), but their further development has not been seen. CLASS VI. RETICULARIA, Carpenter, 1862. (Fora /Rinifcra, Auct., Thalamophora. Hertwig). Characters. Gymnomyxa in which the dominating amoeba- phase, often of great size (an inch in diameter), has an irregular form, and a tendency to throw out great trunks of branching and often anastomosing filamentous pseudopodia, and an equally strong tendency to form a shell of secreted membrane or secreted lime or of agglutinated sand particles (only in one genus of secreted silex) into which the protoplasm (not in all ?) can be drawn and out of and over which it usually streams in widely spreading lobes and branches. One nucleus is present, or there are many. A contrac tile vacuole is sometimes, but not as a rule, present (or at any rate not described). Reproduction is by fission and (as in some other Protozoa) by the formation of peculiar bud-spores which remain for a time after their formation embedded in the parental proto plasm. Xo multiple breaking up into spores after or independent of the formation of a cyst is known. Marine and freshwater. The Keticularia are divisible into several orders. The marked peculiarity of the shell structure in certain of these orders is only fitly emphasized by grouping them together as a sub-class Per- forata, in contrast to which the remaining orders stand as a sub-class Imperforata. The distinction, however, is not an ab solute one, for a few of the Lituolidea are perforate, that is, are sandy isomorphs of perforate genera such as Globigerina and Rotalia. FIG. IX. Gromiidea (Reticularia membranosa). 1. Diplophryi Archeri, Barker, a, nucleus; b, contractile vacuoles; c, the yellow oil-like body. Moor pools, Ireland. 2. Gromia ovijonnis, Duj. a, the numerous nuclei ; near these the elongated bodies represent ingested Diatoms. Freshwater. 3. Sheyheardella txniiformis, Siddall (Quart. Jour. Micr. Sci., 1880); x 30 diameters. Marine. The protoplasm is retracted at both ends into the tubular case. , nucleus. 5. Shep- heardella txniiformis ; x 15 ; 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 Wrirjhtianum, Archer, showing membranous shell encrusted with foreign particles. Moor pools, Ireland. I l. Diaphorophodon mobile, Archer, a, nucleus. Moor pools, Ireland. SUB-CLASS A. Imperforata. Characters. Shell-substance not perforated by numerous aper tures through which the protoplasm can issue, but provided with only one or two large apertures, or in branched forms with a few such apertures. ORDER 1. GROMIIDEA, Brady. Characters. Shell or test membranous, in the form of a simple sac with a pseudopodial aperture either at one extremity or at both. Pseudopodia thread-like, long, branching, reticulated. Marine and freshwater. Fain. 1. MOXOSTOMIXA, with a single aperture to the shell.