Online Encyclopedia

adaptation to a semipelagic existence correlated with the frothy cytoplasm (fig. I (I)). Actinophrys sol and Actinosphaerium eichhornii (fig. 2), known as See also:

sun animalcules to the older microscopists, See also:

FLOAT (in O. Eng. floc and flota, in the verbal form f eotan; the Teutonic root is flut-, another form of flu-, seen in " flow," cf. " fleet "; the root is seen in Gr. a-M e, to sail, Lat. pluere, to rain; the Lat, fluere and fluctus, wave, is not connect

float freely in stagnant or slow-flowing See also:

WATERS, TERRITORIAL

waters, and Alyriophrys is able by an investment of See also:

long fiagelliform See also:

CILIA (plural of Lat. cilium, eyelash)

cilia to swim freely. The See also:

MAJORITY (Fr. majorite; Med. Lat. majoritas; Lat. major, greater)

majority, however, lurk among confervae or the See also:

LIGHT

light debris of the bottom See also:

OOZE (O. Eng. wdse, cognate with an obsolete waise, mud; cf. O. Nor. veisa, muddy pool)

ooze; and come under the See also:

head of " sapropelic " rather than pelagic organisms. The See also:

BODY

body is usually of See also:

CONSTANT, BENJAMIN (1845-1902)

constant spherical form in relation to the floating See also:

HABIT (through the French from Lat. habitus, from habere, to have, hold, or, in a reflective sense, to be in a certain condition; in many of the English senses the French use habitude, not habit)

habit. Nuclearia, however, shows amoeboid changes of general outline. The pseudopods are retractile, the axial filament being absorbed as the filament grows shorter and thicker and disappearing when the See also:

PSEUDOPOD, PSEUDOPODIUM

pseudopod merges into the ectoplasm, to he reformed at the same See also:

time with the pseudopod.

There is often a distinction, clear, but never See also:

sharp, between the richly vacuolate, almost frothy ectoplasm and the denser endoplasm. One or more contractile vacuoles may protrude from the ectoplasm. The endoplasm contains the nucleus or nuclei. The nucleus when single may be central or excentric: in the latter See also:

case, the endoplasm contains a clear central See also:

SPHERE (Gr. vclsa?pa, a ball or globe)

sphere (" centrosome ") on which abut the axial filaments of the pseudo-pods. The ectoplasm contains, in some See also:

SPECIES

species, constantly (Raphidiophrys viridis) or occasionally (A ctinosphaerium), See also:

green cells belonging to the genera Zoochlorella and Sphaerocystis, both probably—the latter certainly—vegetative stages of a Chlamydomonad (See also:

FLAGELLATA

FLAGELLATA, q.v.) and of symbiotic significance. The Heliozoa can move by See also:

ROLLING

rolling over on their extended pseudo-pods; Acanthocystis ludibunda traversing a path of as much as twenty times its See also:

DIAMETER (from the Cr. &a, through, µErpov, measure)

diameter in a See also:

minute, according to Penard. several species (e.g. Raphidiophrys elegans) remain associated by the See also:

union of their pseudopods, whether into social aggregates (due to approximation) or " colonies " due to lack of separation1 ....a 8 after fission, is not accurately known. The multinuclear species Actinosphaerium eichhornii (fig. 2), normally apocytial (i.e. the nuclei See also:

DIVIDE

divide repeatedly without See also:

DIVISION (from Lat. dividere, to break up into parts, separate)

division of the cytoplasm), may increase in See also:

SIZE

size by the See also:

FUSION

fusion (" plastogamic ") of small individuals. If a large specimen be cut up or fragment itself under irritation, the small ones so produced soon approach one another and fuse completely. Reproduction.—Binary fission has been repeatedly observed; in some cases one or both of the daughter cells may swim for a timeas a biflagellate zoospore (fig. i (6, 7)). The See also:

PROCESS

process may take See also:

PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

place when the See also:

CELL (from Lat. cella, probably from an Indo-European kal —seen in Lat. celare, to hide; another suggestion connects the word with Lat. cera, wax, taking the original meaning to refer to the honeycomb)

cell is naked or after preliminary encystment.

Budding has been well studied in Acanthocystis; the cell nucleus divides repeatedly and most of the daughter nuclei pass to the periphery, aggregate See also:

PART

part of the cytoplasm, and with it are constricted off as See also:

INDEPENDENT

independent cells; one nucleus remains central and the process may be repeated. The detached bud may assume the typical character after a See also:

SHORT, FRANCIS JOB (1857– )

short amoeboid (lobose) See also:

STAGE (Fr. 6/age; from Lat. stare, to stand)

stage, sometimes preceded by See also:

REST (O. Eng. rest, reste, bed, cognate with other Teutonic forms, e.g. Ger. Rast, Riiste, rest, and probably Gothic Rasta, league, i.e. resting or stopping place)

rest, or it may develop 2 flagella and swim off (fig. T (6)). Brood formation is only known here in relation to a syngamic process; this is a sharp contrast to Proteomyxa (q.v.) where brood-formation is the commonest mode of reproduction, and plasmodium-formation, rare indeed, is the nearest approach to syngamy observed. Indeed, if we knew the See also:

LIFE

life-See also:

HISTORY

history of all the species this difference in the life See also:

cycle would be a convenient See also:

CRITICAL (in alphabetical order of authors)

critical character. Equal conjugation was demonstrated fully by F. Schaudinn in Actinophrys; two individuals approach and enter into See also:

close contact, and are surrounded by a See also:

COMMON

common cyst See also:

wall. The nucleus of either male divides; and one nucleus passes to the See also:

SURFACE

surface at either See also:

side, and is budded off with a small portion of the cytoplasm as an abortive cell ; the two remaining nuclei which are " first See also:

COUSINS, SAMUEL (18o1-1887)

cousins " in cellular relationship now fuse, as is the case with the cytoplasts. The resulting coupled cell or zygote divides into two, which again encyst. Actinosphaerium (fig. 2) shows a still more remarkable process, fully studied by R. Hertwig.

The large multinucleate See also:

animal withdraws its pseudopods, its vacuoles disappear, it encysts and its nuclei diminish in number to about th partly by fusion, 2 and 2, probably by digestion of the majority. Within the See also:

PRIMARY

primary cyst the body is now resolved into nuclear cells, which again surround themselves with secondary cysts. The cell in each secondary cyst divides (by karyokinesis), and these See also:

SISTER

sister cells, or rather their offspring, pair in much the same way as the individual cells of Actinophrys—the See also:

CHIEF (from Fr. chef, head, Lat. caput)

chief difference is that after the first division and budding off of, a rudimentary cell, a second division of the same character takes place, with the formation of a second rudimentary cell, which is the niece of the first, absolutely in the same way as the 1st and 2nd polar bodies are formed in the maturation of the ovum in Metazoa. The actual pairing cells are thus second cousins, See also:

GREAT

great-granddaughters of the See also:

ORIGINAL

original cell of the secondary cysts. Complete fusion now takes place to form the coupled cell, which is now contracted and forms a gelatinous wall within the siliceous secondary cyst wall (fig. 2 (14)). During a resting stage nuclear divisions occur and finally a brood of See also:

young 1-nuclear Actinosphaerium leave the cyst. See also:

CLASSIFICATION (Lat. classis, a class, probably from the root cal-, cla-, as in Gr. icaMce, clamor)

Classification. Aphrothoraca. Body naked. Actinophrys Ehrb. (fig.

1 (I)) (nucleate), Actinosphaerium See also:

Stein plurinucleate (fig. 2 (I)), Camptonema (plurinucleate) Schaud., Dimorpha See also:

GRUBER, JOHANN GOTTFRIED (1774-1851)

Gruber (some-times 2 flagellate). I. Chlamydophora. Investment gelatinous. Astrodiscus. II. Chalarothoraca. Body protected by an investment of spicules or fibre scattered or approximated, never fused into a continuous skeleton. § 1. Spicules netted or See also:

FREE

free in the protoplasm. Heterophrys See also:

Arch.

(fig. 1 (3)), Raphidiophrys Arch. (fig. 1 (4)), Pinacodocystis, Hertw. and Less. § 2. Spicules approximated radially. Pinaciophora Greeff, Pompholyxophrys Arch., Lithocolla F. E. See also:

SCHULTZE, MAX JOHANN SIGISMUND (1825-1874)

Schultze, Elaeorhanis Greeff (in the two foregoing genera the spicules represented by See also:

sand granules), Acanthocystis See also:

CARTER, ELIZABETH (1717-1806)

Carter (fig. i (5)), Pinacocystis (?) Hertw. and Less, Myriophrys Penard. (Astrodisculus). 2. Free Elaster, Grimin, Choanocystis.

End of Article: HELIOZOA

Additional information and Comments

There are no comments yet for this article.

» Add information or comments to this article.

Please link directly to this article:
Highlight the code below, right click, and select "copy." Then paste it into your website, email, or other HTML.

Site content, images, and layout Copyright © 2006 - Net Industries, worldwide.
Do not copy, download, transfer, or otherwise replicate the site content in whole or in part.

Links to articles and home page are always encouraged.

[back]
HELIOTROPE, or TURNSOLE

[next]
HELIUM (from Gr. i)Xcor, the sun)