. A manual of elementary zoology . Zoology. THE PROTOZOA AS PARASITES OF MAN 159 the hollow side, an undulating membrane, one contractile vacuole in the hinder part of the body, and a remarkable permanent anus, lined with ectoplasm, at the hind end. The related N. faba has been found in the intestine of a man suffering from dysentery, but it is doubtful whether it was the cause of the disease. More numerous and conspicuous than either of these is Opalina ranarum, a flat, oval, pale-straw-coloured ciliate of very large size (i mm. long), uniformly covered with equal cilia, and without mouth, pe
. A manual of elementary zoology . Zoology. THE PROTOZOA AS PARASITES OF MAN 159 the hollow side, an undulating membrane, one contractile vacuole in the hinder part of the body, and a remarkable permanent anus, lined with ectoplasm, at the hind end. The related N. faba has been found in the intestine of a man suffering from dysentery, but it is doubtful whether it was the cause of the disease. More numerous and conspicuous than either of these is Opalina ranarum, a flat, oval, pale-straw-coloured ciliate of very large size (i mm. long), uniformly covered with equal cilia, and without mouth, peristome, contractile vacuole, or trichocysts. It has many nuclei, unlike those of other Ciliata in being all of one kind. The life-history is also very unlike that of other Ciliata. Nuclei and cytoplasm divide independently (the latter alternately in a longitudinal and a transverse direction), and during the greater part of the year keep pace with one. Fig. 99.—Ciliata from the rectum of the frog. A, Opalina ranarum ; B, Balantidium entozoon ; C, Nyctotherus cordiformis. Anus; , contractile vacuoles; ec, ectoplasm; en., endoplasm; g., gullet; meg:, meganucleus ; mi., niicronucleus ; nu., nuclei; v., vestibule or peristome. another and with growth, so that the appearance of the mature animals remains the same; but in the spring the division of the cytoplasm gains, so that small individuals with 3-6 nuclei result. It is said that at this time a portion of the chromatin of the nuclei passes in granular or "chromidial" form (p. 83) into the cytoplasm, where it condenses to form new nuclei while the old ones perish. The little individuals now encyst, casting out from each nucleus two successive masses of chromatin which are destroyed. The cysts are passed by the frog into the water and there swallowed by tadpoles, in which they hatch and their cytoplasm divides to form uninuclear gametes. These conjugate, and the zygote encysts. From the cyst emerges a uni- nucl
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectzoology, bookyear1920
