Text-book of comparative anatomy . nsider the Hydroid form as a youngstage of the Medusa form. Nutritive polyp and Medusa are one sister develops further than the other and reproduces sexu-ally, while the latter remains sterile. There are two other methods of development to be derived fromthe alternation of generations of the Hydro-Medusce. There areHydroid stocks in which the sexual persons do not detach themselves 116 COMPARATIVE ANATOMY CHAP. from the stock, but remain connected with it as medusoid the fertilised eggs of such Hydroids other Hydroids are produced.
Text-book of comparative anatomy . nsider the Hydroid form as a youngstage of the Medusa form. Nutritive polyp and Medusa are one sister develops further than the other and reproduces sexu-ally, while the latter remains sterile. There are two other methods of development to be derived fromthe alternation of generations of the Hydro-Medusce. There areHydroid stocks in which the sexual persons do not detach themselves 116 COMPARATIVE ANATOMY CHAP. from the stock, but remain connected with it as medusoid the fertilised eggs of such Hydroids other Hydroids are the other hand there are Hydro-Medusa in whose whole life cycleno attached Hydroid stock is developed. From the fertilised egg of sucha Craspedote Medusa another sexual Medusa is produced, often after aseries of metamorphoses. In the Discomedusce also a kind of alternation of generations fertilised egg may develop into a young attached Medusa, whichreproduces asexually by axial budding (strobilation, Fig. 81, p. 107). Fio. SS.—Nausithoe. pr, Perradii; ir, interradii; ar, adradii; sr, subradii; rl, marginal lobes ;t, tentacles; gf, gastral filaments; m, circular muscle of the subumbrella; sfc, sensory bodies(rhopalia); g, sexual glands (gonades); in the middle the oral cross. or by lateral budding1. The constricted young Medusae (ephyr^e),whose organisation, but for absence of gonades, is essentially the sameas that of Naustthoe (Fig. 88), undergo a more or less complicatedmetamorphosis, till they again become adult sexually mature , however, the organism which multiplies asexually is really ayoung stage of the sexually differentiated Medusa, not a sister as inthe Hydro-Medusa. The young Scyphistoma does not need to multiplyasexually. It can detach itself from the stem and develop direct intoa Medusa. There are also very many free-swimming Scypho-Meduscefrom whose fertilised eggs a new Medusa is produced again directwithout the intervention of an atta
Size: 1595px × 1567px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
