. Animal parasites and messmates. Parasites. TRANSMIGRATIONS AND METAMORPHOSES. 191 ever see lier retrograde tlius from a more complicated organization to one more simple ?" That which this great observer did not dare to believe has yet been realized, and in many cases development is clearly recm-rent. Led by a marvellous instinct, and obeying an irre- vocable mission, the distomidse, as well as the monostomidae, and others besides them, when they claim an asvlmn from molluscs, introduce into the living body of their new host, not an isolated embryo, but a 3'Oung animal already impregnate
. Animal parasites and messmates. Parasites. TRANSMIGRATIONS AND METAMORPHOSES. 191 ever see lier retrograde tlius from a more complicated organization to one more simple ?" That which this great observer did not dare to believe has yet been realized, and in many cases development is clearly recm-rent. Led by a marvellous instinct, and obeying an irre- vocable mission, the distomidse, as well as the monostomidae, and others besides them, when they claim an asvlmn from molluscs, introduce into the living body of their new host, not an isolated embryo, but a 3'Oung animal already impregnated with a rich posterity; if she remam mistress of the situation, this posterity will forcibly invade the various organs, without any consideration whether their host may not give way under the weight of this sudden invasion. Fig. 41 represents one of these worms which proceeds from a cili- ated embryo, and encloses by the side of its digestive tube cercariae in different degrees of develop- ment. In front, we see one pro- vided with eyes and a tail; behind, we see others which are j^ounger; among these ciliated embr^^os, wandering without guidance and without a compass in the midst of their ocean, but few will reach the land, or, in other words, will find the 10. Fig. 41.—]\[onostoraum verru- cosum, Sporocyst with Cer- carife. In front is the mouth, in the middle the digestive canal, and around the diges- tive canal are young ones, under the form of Cercariaj in process of Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Beneden, M. van (Pierre Joseph), 1809-1894. New York, D. Appleton and Company
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectparasit, bookyear1876
