Outlines of zoology . complished, the Infusorians separate, andnuclear reconstruction begins. The fertilised micronucleus divides intotwo (F), and each half divides again (G), so that there are four in eachcell. Two of these form the macronuclei of the two daughter-cellsinto which the Infusprian proceeds to divide (H); the other two formthe micronuclei, but before another division occurs each has againdivided. Thus each daughter-cell contains a macronucleus and twomicronuclei. Fifth Type of Protozoa—Vorticella Vorticella, or the bell-animalcule, is a type of thoseciliated Infusorians in which
Outlines of zoology . complished, the Infusorians separate, andnuclear reconstruction begins. The fertilised micronucleus divides intotwo (F), and each half divides again (G), so that there are four in eachcell. Two of these form the macronuclei of the two daughter-cellsinto which the Infusprian proceeds to divide (H); the other two formthe micronuclei, but before another division occurs each has againdivided. Thus each daughter-cell contains a macronucleus and twomicronuclei. Fifth Type of Protozoa—Vorticella Vorticella, or the bell-animalcule, is a type of thoseciliated Infusorians in which the cilia are restricted to aregion round the mouth (Peritricha). VORTICELLA. 97 Description.—Groups of Vorticella, or of the compoundform Carchesium, grow on the stems of fresh-water plants,and are sometimes readily visible to the unaided eye aswhite fringes. In Vorticella each individual suggests aninverted bell with a long flexible handle. The base of thestalk is moored to the water-weed, the bell swings in the. Fig. 42.—Vorticella.—MXRX Butschli. 1. Structure. N., Macronucleus; «., micronucleus; , con- tractile vacuole ; ?«., mouth ;/.»., food vacuole ; v., vestibule. 2. Encysted individual. ^ 3, Division. 4. Separation of a free-swimtnin^ unit—the result of a division. 5. Formation of eight minute units (m^-.). 6. Conjugation of microzooid (wr^.) with one of normal size water, now jerking out to the full length of its tether, andagain cowering down with the stalk contracted into a closeand delicate spiral. In Carchesium the stalk is branched,and each branch terminates in a bell. Up the stalk thereruns, in a slightly wavy curve, a contractile filament, which,in shortening, gives the non-contractile sheath a spiral contractile filament, under a high power, may exhibita fine striation. (A similar striated structure is seen in7 98 PHYLUM PROTOZOA—THE SIMPLEST ANIMALS. some Amoebae, Gregarines, spermatozoa, etc., and of a muchcoarser type in striped
Size: 1563px × 1599px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
