Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 TKEMATODA. cases (Tristomui)i coccineuin) transverse rows of bristles are found. Paired eyes are frequently present. In some species the elongated body presents a kind of external segmentation. They are for the most part ectoparasitic, to a certain extent like the Hirudinea, and they develop directly without alternation of generations from eggs which are usually hatched in the locality inhabited by the mother. Sometimes the development is a metamorphosis (Polystomum), and the young larva
Elementary text-book of zoology (1884) Elementary text-book of zoology elementarytextbo0101clau Year: 1884 TKEMATODA. cases (Tristomui)i coccineuin) transverse rows of bristles are found. Paired eyes are frequently present. In some species the elongated body presents a kind of external segmentation. They are for the most part ectoparasitic, to a certain extent like the Hirudinea, and they develop directly without alternation of generations from eggs which are usually hatched in the locality inhabited by the mother. Sometimes the development is a metamorphosis (Polystomum), and the young larva? live in another place. The development of Polystomum integerri- mum from the bladder of the frog is the best known, owing to the researches of E. Zeller '°- (figs. 258, ). The production of eggs begins W in the spring, when the frog awakes from hibernation and proceeds to pair. It lasts from three ' to four weeks. It is easy then to observe the Poli/sto- •mea in the process of reciprocal copulation. When the are being laid, Ov eggs FIG. 259.—Egg with embryo (a, and hatched larva (6) of PoJystomim/ integerrimum ; ZU-, ,1 operculum (after E. Zeller)! forces the
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