. Zoology : for students and general readers . Zoology. 144 ZOOLOGY. The Turbellaria are hermaphroditic, the ovaries and testes â with the accessory apparatus (Fig. 95) being present in the same individual. Little is known of the development of the flat-worms. In a common marine Planariau, Stylochus elliptica (Girard), which is about two centimetres long, and lives under stones between tide-marks, north of Cape Cod, the eggs are depos- ited in May and June, in a thin, viscid band, on stones and sea-weeds. The eggs undergo total segmentation in four or five days after they are laid. The larva i
. Zoology : for students and general readers . Zoology. 144 ZOOLOGY. The Turbellaria are hermaphroditic, the ovaries and testes â with the accessory apparatus (Fig. 95) being present in the same individual. Little is known of the development of the flat-worms. In a common marine Planariau, Stylochus elliptica (Girard), which is about two centimetres long, and lives under stones between tide-marks, north of Cape Cod, the eggs are depos- ited in May and June, in a thin, viscid band, on stones and sea-weeds. The eggs undergo total segmentation in four or five days after they are laid. The larva is round, ciliated, with a caudal flagellum. In eight or ten days after the larva has hatched, it stops swimming about, and becomes a "mummy-like body," which Girard calls a "; In this state it floats about in the water. Its further his- tory is unknown. In Leptoplana (Polycelis), according to Keferstein, the yolk undergoes total segmentation as in Stylochus; the outer layer of cells forms a blastoderm which surrounds the more slowly growing cells within. Keferstein describes and figures the various stages by which the spherical cili- ated embryo attains the form of the adult, whose devel- opment seems to be less in the nature of a metamorphosis than that of Stylochus. The Planarians also in some species mul- tiply by fission, and when cut into pieces, according to H. J. Clark, each piece may eventually become a well-formed Planarian. Clark figures in his " Mind in Nature" two Planarians derived from two sections of Dendrocoelum lacteum, which became fully developed within eleven days after the opera- tion. Several Turbellarians are known to undergo spontaneous fission. Catenula lemnce Dug^s, by transverse di- "^ision, forms chain-like aggregations, and 'oi2'"'6dMivi6ton' * South African species, C. quaterna, of -After schmarda. Schmarda, has been found by him to have the same habit. Fig. 96 represents two indi
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectzoology, bookyear1879
