Medusae of the world . d. Entoderm of manubrium, gonads, and bell-margin brownish-yellow, other parts colorless. Hydroid.—That which is probably the hydroid of this medusa was first found by Parsons,1880, and first described by Bourne, 1884. It grows in colonies of 2 or 3 polypites arising fromcommon base and is attached to the under sides of leaves, etc., floating or growing in thewater of the lily-tank in Regents Park. The polypites are only about mm. long and arecylindrical with rounded peristomes devoid of tentacles. The mouth is a simple terminalopening. There is no perisarc, but the
Medusae of the world . d. Entoderm of manubrium, gonads, and bell-margin brownish-yellow, other parts colorless. Hydroid.—That which is probably the hydroid of this medusa was first found by Parsons,1880, and first described by Bourne, 1884. It grows in colonies of 2 or 3 polypites arising fromcommon base and is attached to the under sides of leaves, etc., floating or growing in thewater of the lily-tank in Regents Park. The polypites are only about mm. long and arecylindrical with rounded peristomes devoid of tentacles. The mouth is a simple terminalopening. There is no perisarc, but the sides and bases of the polypites are incased in a coatingof sticks, detritus, etc., caught apparently in slime. The oral ends are, however, free fromthis detritus. Planula-shaped buds are produced upon the basal halves of the sides of thepolypites, and these are set free and settle down to form new colonies of hydroids, very muchas in Microhydra ryderi. The medusa-bud is produced at the oral end of the polypite, both. CRASPEDACUSTA. 365 ectoderm and entoderm taking part in its formation. Thus each polypite appears to give riseto but one medusa, although the detachment of the medusa and future fate of the polypite hasnot been observed. We must bear in mind that it is not yet certain that this hydroid is actuallythe asexual generation of C. sowerbii. The young stages in the development of the free medusa, found in the lily-tank, havebeen studied by Lankester, 1881 (Quart. Journ. Microscop. Soc. London, vol. 21, p. 194,5 figs.). When the embryo is less than 1 mm. in diameter the body is globular with 8 verysmall tentacles, 4 radial, 4 interradial, and 2 marginal lithocysts. The velum is present as adiaphragm-like membrane at the bases of the tentacles; but inside of, and separate from,the velum there is said to be a peculiar imperforate membrane which completely closes thebell-cavity. The manubrium is well developed at this stage and there are 4 radial-canals. Haec
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectcnidari, bookyear1910
