. A manual of zoology. PHYLUM PLATYHELMINTHES 137 are no cilia on the surface, and a well-developed enteric canal is always present. A remarkable series of metamorphoses, such as that which has been de- scribed in the liver-fluke, is characteristic of the internally parasitic forms; in the ectoparasitic or externally parasitic Tre- matodes development is direct, the young animal when it escapes from the egg differing little from the adult except in size. 2. THE TUHBELLAKIA The Turbellaria are a class of flat-worms which, though for the most part non-parasitic,resemble the Trematodes very close
. A manual of zoology. PHYLUM PLATYHELMINTHES 137 are no cilia on the surface, and a well-developed enteric canal is always present. A remarkable series of metamorphoses, such as that which has been de- scribed in the liver-fluke, is characteristic of the internally parasitic forms; in the ectoparasitic or externally parasitic Tre- matodes development is direct, the young animal when it escapes from the egg differing little from the adult except in size. 2. THE TUHBELLAKIA The Turbellaria are a class of flat-worms which, though for the most part non-parasitic,resemble the Trematodes very closely, the chief difference being the presence of a coating of vibrating cilia, and the absence, in the majority, of suckers. The leaf form is the prevailing one (Fig. 72), but in many the body is elongated and ribbon- like, or subcylindrical. In some the anterior end is retractile, and may be everted as. Fig. 72. —General plan of the structure of a Triclad Turbellarian. en, brain; e, eye; g; ovary; i\, median limb of the intestine; iz, left limb; is, right limb; /;/, longitudinal nerve-cord; in, mouth; od, oviduct; pit, pharynx; t, testes; r>, tentacles; vd, vas deferens; //.uterus; <?, ejaculatory duct; £ , vagina; rf Q , common genital aperture. (After Von Graff.). 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 Parker, T. Jeffery (Thomas Jeffery), 1850-1897; Haswell, William A. (William Aitcheson), 1854-1925. New York, The Macmillan Company; London, Macmillan & Co. ,Ltd.
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