Identifier: royalnaturalhist612lyde (find matches)
Title: The royal natural history
Year: 1893 (1890s)
Authors: Lydekker, Richard, 1849-1915 Sclater, Philip Lutley, 1829-1913 Frostick, W. B., former owner. DSI Brooks, W. T., former owner. DSI
Subjects: Zoology Natural history
Publisher: London and New York : Frederick Warne & Co.
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Smithsonian Libraries

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FLAT-WORMS. 459 The Flat-Worms,—Class Platyhelminthes. The flat-worms are characterised by the absence of a distinct vascular system,and by the alimentary canal being either absent or with no posterior outlet. Anervous system is developed, consisting either of a network of nerves, or some-times of a distinct brain and lateral chords. The excretory organs are composedof fine tubules opening to the exterior, and the body-cavity is reduced to a set ofslits in the tissues. For the most part the sexes are united in one individual.Sometimes a sexual reproduction occurs, accompanied by an alteration of genera-tions. There are three orders of flat-worms, namely, the tape - worms, thetrematodes, and the turbellarians.
Text Appearing After Image:
CROSS-BEARING NE.MERTINE (1olia craciijrro) UN A CORAL (nat. size). Tape-Worms,—Order Cestoda. The members of this extensive group are internal parasitical worms withthe body divided into a number of segments. There is no trace of an alimentarycanal, nutriment being obtained by the absorption of juices through the entiresurface of the body. The head is furnished with suckers, or hooks, or both, by meansof which the worm adheres to the walls of the intestine of the host it infests.The nervous system consists of a ganglion in the head, and a cord on each side.As a well-known example, we may take Taenia saginata, one of the human tape-worms; and since its structure and the phases through which it passes in thecourse of its development are thoroughly known, a detailed discussion of itscharacteristics will serve as an introduction to the study of the group. In its 460 WORMS. mature state this worm, which spends this stage of its existence in the humanintestines, may reach a length of 5 o

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