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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flower-animalcule (magnified 200 times). 443 WORMS. The Thread-Worms, or Round-Worms,—Class Nematohelminthes. These worms are characterised by having a thread-like body, covered withtough, elastic integument, but usually showing no distinct traces of being dividedinto segments like those of leeches and earth-worms, and possessing no trace oflimbs. The sexes are generally distinct. The group is divided into the threeorders Acanthocephali, Nematoidea, and Chaetognatha. Spiny-Headed Thread-Worms,—Order Acanthocephali. In this order is contained the single genus Echinorhynchus, which is appro-priately named for animals possessing a protrusible proboscis, armed with severalrows of backwardly-directed spines. The chief character in which this order
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si-iny-headed THREAD-WORM, a, Nat. size; b, Heart enlarged. differs from the next is the lack of any special alimentary canal and digestiveapparatus. In the adult stage the species of Echinorhynchus are found in theintestines of vertebrates; the large species figured above (E. gigas) infesting thepig. But in order to reach its final residence in this host, it has to spend its early THREAD- WORMS. 449 days in the grub or maggot of the cockchafer and allied beetles. These latter arerooted up and devoured by pigs, which thus unconsciously swallow the worm.Similarly, E. proteus of various fish lives in an immature state in the intestine ofthe water-shrimp, which swallowed it while still in the egg; and E. moni-liferus, which occurs adult in such rodents as hamsters and voles, lives duringthe larval state in beetles. Another species, E. polymorphic*, has to be transplantedfrom the body of the water-shrimp into that of a duck to reach maturity. Typical Thread-Worms,—Order Nematoidea. The

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