The porifera and coelentera . brium. The sexes are of the by Gemmation.—A medusoidof the type indicated above is either budded (a) from a hydroid(Syncoryne), or from a blastostyle (Tubularia), or from thehydrocaulus (Bougainvillea), or, with the intermediation of ashort stem, from the hydrorhiza (most Perigonimus), or (//) from amedusoid (Sarsia), either from the manubrium (Fig. 25), orfrom the margin of the bell, at the end of the perradial canals(Codonium). Although in many cases niedusoids have not beentraced to hydroids, no medusoid of this group has been found
The porifera and coelentera . brium. The sexes are of the by Gemmation.—A medusoidof the type indicated above is either budded (a) from a hydroid(Syncoryne), or from a blastostyle (Tubularia), or from thehydrocaulus (Bougainvillea), or, with the intermediation of ashort stem, from the hydrorhiza (most Perigonimus), or (//) from amedusoid (Sarsia), either from the manubrium (Fig. 25), orfrom the margin of the bell, at the end of the perradial canals(Codonium). Although in many cases niedusoids have not beentraced to hydroids, no medusoid of this group has been foundto develop directly from the ovum. THE HYDROMEDUSAE If, as seems probable, the product of the fertilised ovum ofthe Authomedusae is always a hydroid, there is an invariablealternation of an asexual generation (the hydroid) with a sexualgeneration (the medusoid); this alternation of generations, ormetagenesis (Brooks, 14), is not disturbed by the fact that the sexualgeneration may in a few cases reproduce asexually (Sarsia)..
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Keywords: ., bookcentury1900, bookdecade1900, booksubje, booksubjectctenophora
