. The study of animal life . nies ( star-corals Astrcea, brain-coralMcEandrind); and (b) Dead-mens-fingers {Alcyomuf?t) andothers like it, also with related corals, the organ-pipecoral {Tubip07-a miisica) and the noble coral of com-merce [Corallium rubrum). Third Series— The Ctenophores, which are markedly contrasted with corals, being free and light and active. Many { Beroe and Pleurobrachia) swarm in our seas in summer, iridescent in daylight, phosphorescent at night. They differ in many O 236 TJu Study of Animal Life part hi ways from other Coelenterates, thus the characteristi
. The study of animal life . nies ( star-corals Astrcea, brain-coralMcEandrind); and (b) Dead-mens-fingers {Alcyomuf?t) andothers like it, also with related corals, the organ-pipecoral {Tubip07-a miisica) and the noble coral of com-merce [Corallium rubrum). Third Series— The Ctenophores, which are markedly contrasted with corals, being free and light and active. Many { Beroe and Pleurobrachia) swarm in our seas in summer, iridescent in daylight, phosphorescent at night. They differ in many O 236 TJu Study of Animal Life part hi ways from other Coelenterates, thus the characteristicstinging cells are modified into adhesive first and second series, separated by differences of structureand development, are yet parallel. In both there are polype-types ;in both medusoid types ; in both there are single individuals andcolonies of individuals; in both there are corals. We maycompare a Hydra with a sea-anemone, a medusoid with a jelly-fish, a hydroid colony with Dead-mens-fingers, Millepores with. Fig. 42.^The alternation of generations in the common jellj-tish Aurelia. i»the free-swimming embryo, 2, the embryo settled down ; 3, 4, 5, 6, the de-veloping asexual stages, or hydra-tubse; 7, 8, the formation of a pile ofindividuals by transverse budding; 9, the liberation of these individuals;10, II, their progress towards the free-swimming sexual medusa form. (Fromthe Evolution of Sex ; after Haeckel.) the commoner reef-corals. Moreover, we may compare a medusoidliberated from a hydroid v^ith Aurelia liberated from its fixed polype-stage, and permanently-free medusoids with jellyfishes like are physiological parallels. The sedentary polypes are somewhat sluggish, with a tendencyto bud and to form shells or skeletons of some kind. The free-swimming medusoid types are active, they rarely bud, they do notform skeletons, but their activity is sometimes expressed in CHAP. XV Backboneless Afiimals 227 phosphorescence, and their fuller life is
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