Text-book of comparative anatomy . evelopment and life-history of the endoparasitic or digeneticTrematoda is remarkably complicated. We choose as an example thetolerably complicated life-history of the fluke, Distoma hepaticum(Fig. 119), which is parasitic in the liver of the sheep, causing the sheep rot. The eggs of the fluke leave the liver of the host by thebile ducts, pass into the intestine, and are ejected with the only develop when they meet with water. In this case theredevelops in the egg shell (A) a ciliated embryo, which leaves the Ill PL AT ODES— LIFE-HISTORY OF TREM
Text-book of comparative anatomy . evelopment and life-history of the endoparasitic or digeneticTrematoda is remarkably complicated. We choose as an example thetolerably complicated life-history of the fluke, Distoma hepaticum(Fig. 119), which is parasitic in the liver of the sheep, causing the sheep rot. The eggs of the fluke leave the liver of the host by thebile ducts, pass into the intestine, and are ejected with the only develop when they meet with water. In this case theredevelops in the egg shell (A) a ciliated embryo, which leaves the Ill PL AT ODES— LIFE-HISTORY OF TREMATODA 169 egg shell and swims about freely (£). It is club-shaped ; at the thickeranterior end it has a small median prominence, behind this an X-shapedeye spot, and under this a ganglion, and further a granulated mass whichis considered to be the intestinal rudiment. We can also recognise 2ciliated cells of the excretory system. The greater mass of the body,however, is formed of germ cells, which are considered to be partheno-. FIG. 119.—Life-history of Distoma hepaticum, after Leuckart. A, Egg with embryo. B,Free-swimming ciliated embryo ; o, eye spot. C, Sporocyst. D, E, and F, Redias ; pit, pharynx ;go, birth aperture; d, intestine. 0, Cercaria ; m-s, oral sucker; n, nerve ganglia ; bs, ventralsucker ; gd, forked branches of the intestine ; cd, glands, \vhose secretion yields the , Encysted young Distoma ; c, cyst. /, Young Distoma in the sheeps intestine. genetic eggs, possessing the capacity of developing without beingfertilised. These germ cells divide (furrow) early, and become cellspheres. The embryos must meet with a water-snail, Limnceus tntncatulus, andpenetrate into its respiratory cavity in order to develop further. Theyhere lose the covering of cilia; the eyes, the ganglion, and the granulatedmass become disorganised. Their bodies represent a pouch, containing 170 COMPARATIVE ANATOMY CHAP. in its interior a certain number of cell spheres which have de
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
