File:Medusae of the world (1910) (14781997185).jpg

Identifier: medusaeofworld02mayo (find matches)
Title: Medusae of the world
Year: 1910 (1910s)
Authors: Mayor, Alfred Goldsborough, 1868-1922 Mayer, Alfred Goldsborough, 1868-1922
Subjects: Jellyfishes Cnidaria
Publisher: Washington, D.C., Carnegie institution of Washington
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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ong thisopen space there is a thick strand of striated muscle fibers. These velar, or marginal, tentacles TRACHYMEDUS^—OLINDIOIDES. 359 are constantly contracting into helical coils and then expanding, and it is apparently theiroffice to capture prey. These contractile tentacles grow out from the marginal bulbs; andindeed, the marginal bulbs are only embryonic or rudimentary velar tentacles. There are 2 lithocysts at the base of the entodermal core of each exumbrella tentacle.Each lithocyst is a closed vesicle, buried in the gelatinous substance on the outer side of thering-canal at a short distance above the bell-margin. Each lithocyst contains a single, refrac-tive, spherical concretion, which is suspended in the cavity of the vesicle and is supportedby and contained within a club-like mass of cells. The lithocyst and concretion are accord-ing to Goto of ectodermal origin, but this may seem improbable in view of their known ento-dermal origin in the closely allied genus Gomonemus.
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Fig. 203.—Olindhides formosa, after Goto, in Mark Anniversary Volume. Showing sector of bell, part of bell-margin,and two views showing mode of origin of 6 radial-canals from manubrium. The manubrium is 4-sided, prismatic, with 4 simple, somewhat flaring lips. 4 canalsarise from the 4 corners of the stomach, but 2 of these primary canals bifurcate immediatelyafter leaving the stomach so that there are 6 radial-canals which reach the circular vessel6o° apart. The ring-canal is broad and gives rise to numerous blindly ending, centripetal 360 MEDUSAE OF THE WORLD. canals, which increase with age. In young medusae 15 mm. in diameter, the centripetal vesselsranged from 11 to 14 per sextant, about 78 in all; whereas in a mature medusa 75 mm. widethe centripetal canals varied from 18 to 23 in the several sextants, or about 120 all told. The 6 gonads are foldings of the subumbrella walls of the 6 radial-canals and extendthroughout the greater portion of their lengths, leaving only a short

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