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medusae

medusae Sentence Examples

  • To establish the exact relationship it is necessary not only to breed but to rear the medusa, which cannot always be done in 1 In some cases hydroids have been reared in aquaria from ova of medusae, but these hydroids have not yet been found in the sea (Browne [Io a]).

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  • - All known hydropolyps possess the power of reproduction by budding, and the buds produced may become either polyps or medusae.

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  • Naked- cation is seen when the eyed Medusae.

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  • A, colony of but grow in all planes Lar;B and C, young and adult medusae.

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  • habit in Hydro medusae.

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  • 23 and 25); and, fourthly, in structure, being hollow or solid, as in the polyp. In some medusae, for instance, the remarkable deep-sea family Pectyllidae, the tentacles may bear suckers, by which the animal may attach itself temporarily.

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  • The sub-umbrella invariably shows a velum as an inwardly projecting ridge or rim at its margin, within the circle .of tentacles; hence the medusae of this sub-class are termed craspedote.

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  • In contrast with the polyp, the longitudinal muscle-system is entirely ectodermal, there being no endodermal muscles in craspedote medusae.

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  • - Muscular Cells of Medusae (Lizzia).

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  • Further, two distinct types of otocyst can be recognized in the Hydro medusae; that of the Leptolinae, in which the entire organ is ectodermal, concrement-cells and all, and the organ is not a tentaculocyst; and that of the Trachylinae, in which the organ is a tentaculocyst, and the concrement-cells are endodermal, derived from the endoderm of the modified tentacle, while the rest of the organ is ectodermal.

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  • - Section of statocyst of Geryonia medusae are the (Carmarina hastata) .

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  • Moreover, all the medusae budded from a given hydroid colony are either male or female, so that even the non-sexual polyp must be considered to have a latent sex.

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  • It has been shown above that polyps are budded only from polyps and that the medusae may be budded either from polyps or from medusae.

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  • Normally the medusae are liberated in quite an immature state; they swim away, feed, grow and become adult mature el individuals.

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  • - Portions of Sections through will be brought about if the Disk of Medusae - the upper one of the medusae mature Lizzia, the lower of Aurelia.

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  • In some cases both free medusae and gonophores may be produced from the same hydroid colony.

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  • This is the case in Syncoryne mirabilis (Allman [1], p. 278) and in Campanularia volubilis; in the latter, free medusae are produced in summer, gonophores in winter (Duplessis [14]).

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  • Again in Pennaria, the male medusae are set free st.c, Statocyst containing the minute cyst.

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  • in a state of maturity, and have ocelli; the female medusae remain attached and have no sense organs.

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  • As medusae are known to bud medusae from the radial canals there is nothing impossible in Aliman's theory, but it cannot be said to have; received satisfactory proof.

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  • It is convenient to distinguish buds that give rise to polyps from those that form medusae.

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  • Hence the budding of medusae exemplifies very clearly a common phenomenon in development, a phylogenetic series of events completely dislocated in the ontogenetic time-sequence.

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  • however, both of the statements and figures of Lang and of the facts to be described presently for medusae (Margellium), it is at least theoretically possible that both germinal and vegetative budding may occur in polyps as well as in medusae.

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  • 2 may be produced on the medusa-buds before the latter are set free as medusae.

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  • B, The lower layer forms a solid G,H, Formation of the medusae.

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  • Hence the Trachylinae are termed " hypogenetic " medusae to contrast them with the metagenetic Leptolinae.

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  • In Cunina parasitica, however, the ovum develops into an actinula, which buds actinulae as before, but only the daughter-actinulae develop into medusae, while the original, parent-actinula dies off; here, therefore, larval budding has led to a true alternation of generations.

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  • founder-polyp) nor its offspring by budding (polyps of the colony) have the power of becoming medusae, but only of producing medusae by budding.

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  • For the most part, polyp and medusa have been regarded as modifications of a common type, a view supported by the existence, among Scyphomedusae (q.v.), of sessile polyp-like medusae (Lucernaria, &c.).

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  • Leuckart in 1848 compared medusae in general terms to flattened polyps.

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  • Mechnikov considered the plate thus formed at the base of the polyp as equivalent to the umbrella, and the body of the polyp as equivalent to the manubrium, of the medusa; on this view the marginal tentacles almost invariably present in medusae are new formations, and the tentacles of the polyp are represented in the medusa by the oral arms which may occur round the mouth, and which sometimes, e.g.

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  • Apart from the weighty arguments which the development furnishes against the theories of Allman and Mechnikov, it may be pointed out that neither hypothesis gives a satisfactory explanation of a structure universally present in medusae of whatever class, namely the endoderm-lamella, discovered by the brothers O.

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  • The evidence against this view may be classed under two heads: first, comparative evidence; hydroids very different in their structural characters and widely separate in the systematic classification of these organisms may produce medusae very similar, at least so far as the essential features of medusan organization are concerned; on the other hydroids closely allied, perhaps almost indistinguishable, may produce gonophores in the one case, medusae in the other; for example, Hydractinia (gonophores) and Podocoryne (medusae), Tubularia (gonophores) and Ectopleura (medusae), Coryne (gonophores) and Syncoryne (medusae),-and so on.

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  • Gonosome with free medusae or gonophores; medusae usually with ocelli, never with otocysts.

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  • In some cases, any polyp of the colony may bud medusae; in other cases, only certain polyps, the blastostyles, have this power.

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  • Until quite recently the hydroids (Gymnoblastea) and the medusae (Anthomedusae) have been classified separately, since the connexion between them was insufficiently known.

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  • Trophosome arborescent, with hydranths of Bougainvillea-type; gonosome free medusae or gonophores, the medusae with solid tentacles in tufts (lophonematous).

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  • Trophosome encrusting with hydranths of Bougainvillea-type, polyps differentiated into blastostyles, gastrozoids and dactylozoids; gonosome free medusae or gonophores.

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  • The typical genus is the well-known hydroid Podocoryne, budding the medusa known as Dysmorphosa; Thamnostylus, Cytaeis, &c., are other medusae with unknown hydroids.

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  • Trophosome, polyps with two whorls of tentacles, the lower filiform, the upper capitate; gonosome, free medusae, with tentacles solid and branched.

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  • Trophosome, polyps with a single whorl of capitate tentacles; gonosome, free medusae, with ten tacles branched, solid.

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  • Corymorphidae (including the medusa-family Hybocodonidae).--, Trophosome solitary polyps, with two whorls of tentacles; gonosome, free medusae or gonophores.

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  • Trophosome, polyps with scattered filiform tentacles; gonosome, medusae or gonophores, the medusae with hollow tentacles.

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  • Turris produces free medusae.

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  • - Tropho- some unknown; gonosome, free medusae, with deep, bell-shaped umbrella, with interradial gonads on the base of the stomach, with branched radial canals, and correspondingly numerous hollow tentacles.

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  • gonosome, free medusae or gonoThe apex of the stomach is prophores.

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  • Trophosome (only known in one genus), polyps with two tentacles forming a creeping colony; gonosome, free medusae with four, six or more radial canals, giving off one or more lateral branches which run to the margin of the umbrella, with the stomach produced into four, six or more lobes, upon which the gonads are developed; the mouth with four lips or with a folded margin; the tentacles simple, arranged evenly round the margin of the umbrella.

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  • It buds medusae, which, however, are as yet only known in an immature condition (C. Mereschkowsky [41]).

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  • The medusae, on the other hand, have the tentacles in four tufts of (in the buds) five each, and thus resemble the medusae of the family Margelidae.

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  • Gonosome with free medusae or gonophores; the medusae typically with otocysts, sometimes with cordyli or ocelli (figs.

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  • Numerous medusae are budded successively within the gonotheca and set free; they swim off and mature in the open sea (Allman [1], p. 48, figs.

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  • Medusae, so-called " meconidia," are budded but not liberated; each in turn, when it reaches sexual maturity, is protruded from the gonotheca by elongation of the stalk, and sets free the embryos, after which it withers and is replaced by another (Allman [1], p. 57, fig.

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  • It is quite possible that some of these medusae will be found to be truly hypogenetic, that is to say, with a life-cycle secondarily simplified by suppression of metagenesis.

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  • - Tropho so m e with stalked hydrothecae; gonosome, free medusae with otocysts and four, rarely six or eight, unbranched radial canals.

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  • - Trophosome only known in one genus (Polycanna), and similar to the preceding; gonosome, free medusae with otocysts and with at least eight radial canals, often a hundred or more, simple or branched.

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  • - Trophosome only known in one genus (Thaumantias), similar to that of the Eucopidae; gonosome, free medusae with otocysts inconspicuous or absent, with usually four, sometimes eight, rarely more than eight, radial canals, simple and unbranched, along which the gonads are developed, with numerous tentacles bearing ocelli and with marginal sense-clubs.

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  • - Trophosome unknown; gonosome, free medusae, with four or six radial canals, bearing the gonads, with numerous tentacles, between which occur sense-clubs, without otocysts.

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  • - Trophosome unknown; gonosome, free medusae of deep form, with radial canals branched in a feathery manner, and After Haeckel, System der Medusen, by permission of Gustav Fischer.

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  • - Trophosome as in the preceding; gonosome, free medusae or gonophores, the medusae with large open otocysts.

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  • a section apart, contrasting sharply with the families next to be mentioned, in none of which are free medusae liberated from the colony, so that only the characters of the trophosome need be considered.) 8.

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  • - Metagenetic colony-forming Hydromedusae, in which the polyp-colony forms a massive, calcareous corallum into which the polyps can be retracted; polyp-individuals always of two kinds, gastrozoids and dactylozoids; gonosome either free medusae or sessile gonophores.

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  • (From Moseley.) irregular coenosarcal canals, the coenosteum may contain, in its superficial portion, chambers or ampullae, in which the reproductive zoids (medusae or gonophores) are budded from the coenosarc.

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  • irregular in form; pores scattered irregularly or in cyclosystems, without styles, with transverse tabulae; free medusae.

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  • The gonosome consists of free medusae in Milleporidae, which are budded from the apex of a dactylozoid in Millepora murrayi, but in other species from the coenosarcal canals.

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  • Medusae with sense-organs represented by otocysts derived from modified tentacles (tentaculocysts), containing otoliths of endodermal origin, and innervated from the ex-umbral nerve-ring.

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  • This order, containing the typical oceanic medusae, is divided into two sub-orders.

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  • The actinula, when free, may multiply by larval budding, but in all cases both the original actinula and all its descendants become converted into medusae, so that there is no alter nation of generations.

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  • The buds become medusae by the direct method of budding described above.

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  • Of doubtful position, but commonly referred to the Trachylinae, are the two genera of fresh-water medusae, Limnocodium and Limnocnida.

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  • It is a re markable fact that all specimens of Limnocodium hitherto seen have been males; it may be inferred from this either that only one polypstock has been introduced into Europe, from which all the medusae seen hitherto have been budded, or perhaps that the female medusa is a sessile gonophore, as in Pennaria.

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  • It buds medusae from the margin of the mouth in May and June, and in August and September the gonads' are formed in the place where the buds arose.

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  • Both these medusae have sense-organs of a peculiar type, which are said to contain an endodermal axis like the sense-organs of Trachylinae, but the fact has recently been called in question for FIG.

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  • In this connexion must be mentioned, finally, the medusae budded from the fresh-water polyp Microhydra.

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  • In view of the great resemblance between Microhydra and the polyp of Limnocodium, it might be expected that the medusae to which they give origin would also be similar.

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  • As yet, however, the medusa of Microhydra has only been seen in an immature condition, but it shows some well-marked differences from Limnocodium, especially in the structure of the tentacles, which furnish useful characters for distinguishing species amongst medusae.

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  • Gonostyles, appendages which produce by budding medusae or gonophores, like the blastostyles of a hydroid colony.

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  • In their most primitive form they are seen in Velella as " gonosiphons," which possess mouths like the ordinary sterile siphons and bud free medusae.

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  • They show every transition between free medusae and sporosacs, as already described for hydroid colonies.

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  • Thus in Velella free medusae are produced, which have been described as an independent genus of medusae, Chrysomitra.

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  • In other types the medusae may be set G, Cavity of the large central and a " trachea.

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  • If fertile they become free medusae or sessile gonophores.

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  • Brooks, " The LifeHistory of the Hydromedusae: a discussion of the Origin of the Medusae, and of the significance of Metagenesis," Mem.

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  • Browne, " On British Hydroids and Medusae," Proc. Zool.

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  • " Biscayan Medusae," Trans.

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  • "Medusae " in Herdman, Rep. Pearl Oyster Fisheries, Gulf of Manaar, iv.

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  • " Deep Sea Medusae," in Reports of the Challenger Expedition, Zool.

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  • Hickson, " The Medusae of Millepora," Proc. Roy.

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  • Murbach and C. Shearer, " On Medusae from the Coast of British Columbia and Alaska," Proc. Zool.

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  • Vertebres) also used the term, as when he spoke of the Medusae as radiata medusaria et anomala; but he preferred the term Radiaria, under which he included Echinodermata and Medusae.

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  • But the most striking of the coast-belt flora are the tropical forms - the palm, mangrove, wild banana (Strelitzia augusta), tree-ferns, tree euphorbia, candelabra spurge and Caput medusae.

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  • Wotton follows Aristotle 1 in the division of animals into the Enaema and the Anaema, and in fact in the recognition of all the groups above given, adding only one large group to those recognized by Aristotle under the Anaema, modifica- namely, the group of Zoophyta, in which Wotton includes the Holothuriae, Star-Fishes, Medusae, Sea-Anemones and Sponges.

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  • We find that polyps may either bud other polyps or may produce medusae, and that medusae may bud medusae, though never, apparently, polyps.

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  • Hence we have a primary subdivision of the colonies of Hydrozoa into those produced by budding of polyps and those produced by budding of medusae.

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  • Medusae capture their prey, consisting of small organisms of various kinds, especially Crustacea, by means of the tentacles which hang out like fishing-lines in all directions.

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  • Medusae thus form an important constituent of the plankton or floating fauna of the ocean, and compete with fish and other animals for the food-supply furnished by minuter forms of life.

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  • divisions of the medusae are characterized by the presence or absence of a velum.

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  • Every possible variety of body-form compatible with the foregoing description may be exhibited by different species of medusae.

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  • (For other figures of medusae see Hydrozoa.) of the mouth.

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  • The sense-organs of medusae are of two classes: (1) pigment spots, sensitive to light, termed ocelli, which may become elaborated into eye-like structures with lens, retina and vitreous body; (2) organs of the sense of balance or orientation, commonly termed otocysts or statocysts.

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  • (For fuller information upon the sense-organs see Hydromedusae.) Medusae are nearly always of separate sexes, and instances of hermaphroditism are rare.

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  • Medusae often have the power of budding, and the buds are formed either on the manubrium, or at the margin of the umbrella, or on an outgrowth or "stolon" produced from the exumbral surface.

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  • Medusae, when they reproduce themselves by budding, always produce medusae, but when they reproduce by the sexual method the embryos produced from the egg grow into medusae in some cases, in other cases into polyps which bud medusae in their turn.

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  • Medusae are exclusively aquatic animals and for the most part marine, but at least two fresh-water species are known.'

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  • A parasitic mode of life is also seen in medusae of the genus Cunina during the larval condition, but the habit is abandoned, in this case, when the medusae become adult.

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  • For figures of medusae see (i) E.

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  • Jena (1879, 2 vols.); (2) Id., "Deep-Sea Medusae," Challenger Reports, Zoology, IV.

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  • The Mollusca agree in being coelomate with the phyla Vertebrata, Platyhelmia (flat-worms), Echinoderma, Appendiculata (insects, ringed-worms, &c.), and others - in fact, with all the Metazoa except the sponges, corals, polyps, and medusae.

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  • When beetles, or medusae, or cats vary, the range of possible variation is limited and determined by the beetle, medusa or cat constitution, and any possible further differentiation or specialization must be in a sense at least orthogenetic - that is to say, a continuation of the line along which the ancestors of the individual in question have been forced.

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  • The oldest is a sandstone, in which are found traces of worms, impressions of Medusae, and shells of Mickwitzia.

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  • In many cases, as, for example, in the Medusae or jelly-fish, the mesogloea may be so thick as to constitute the chief part of the body in bulk and weight.

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  • The development from the egg may be direct, or may take place with an alternation of generations (metagenesis), in which a non-sexual individual, the so-called scyphistoma or scyphopolyp, produces by budding the sexual medusae.

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  • If disturbed they swim about like other medusae until a favourable opportunity presents itself for resuming the sedentary habit.

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  • In these medusae, however, the central nervous system does not form continuous rings, but occurs as four or eight separate con centrations at the margin of the umbrella, centred each round one of the sense-organs (tentaculocysts).

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  • This is a type of germ-layer formation never found in the Hydro medusae, though of universal occurrence in all groups of animals above the Coelentera.

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  • Each taeniola bears a strongly developed longitudinal muscle-band, stated by Claus and Chun to be developed from the endoderm, like the retractor muscles of the anthopolyp, but by other investigators it is affirmed that each retractor muscle of the scyphistoma arises from the lining of a funnel-shaped ectodermal ingrowth (" Septaltrichter ") growing down from the peristome inside each taeniola, in a manner similar to the infundibular cavities of Lucernaria, which in their turn are homologous with the sub f genital cavities of Scypho l A .` medusae.

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  • D, First constriction of the Aurelia scyphistoma to form the pile of ephyrae or young medusae.

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  • Sooner or later, however, the scyphistoma produces free medusae by a process of transverse fission termed strobilization.

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  • It appears, however, that the first of these characters is non-existent, and that the so-called mesenteries are simply the concrescence-areas found in all medusae.

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  • - Medusae more or less cubical in form, with four perradial rhopalia alternating with four interradial tentacles or groups of tentacles; oral arms short; stomach a wide cavity bearing four interradial groups of phacellae and giving off four broad perradial pouches completely separated from each other by four interradial septa (i.e.

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  • - Medusae of deep pyramidal form, often sessile, attached by a stalk developed from the centre of the exumbral surface; rhopalia absent or represented by colletocystophores.

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  • - Free medusae with rhopalia of the normal type; the exumbrella is divided by a circular, so-called coronal groove, into two parts, a central portion, which is conical, thimble-shaped, or domed in form, and a peripheral portion, the pedal zone, which bears the marginal lobes, tentacles and rhopalia; the pedal zone is subdivided into areas termed pedalia, from each of which arises a tentacle or rhopaliurn in the interspace between two adjacent lobes of the margin.

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  • Nausithoe, a small medusa of world-wide distribution, is the type of the subfamily Nausithoidae; the subfamily Linergidae includes the genera Linerges, &c., medusae confined to tropical seas.

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  • - Medusae with umbrella flattened or disk-like, without coronal groove; lips always prolonged into long oral arms. The most prolific and dominant group of the Scyphomedusae, containing two suborders; the Semaeostomae, in which the oral arms remain separate, and the Rhizostomeae, in FIG.

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  • To establish the exact relationship it is necessary not only to breed but to rear the medusa, which cannot always be done in 1 In some cases hydroids have been reared in aquaria from ova of medusae, but these hydroids have not yet been found in the sea (Browne [Io a]).

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  • - All known hydropolyps possess the power of reproduction by budding, and the buds produced may become either polyps or medusae.

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  • Naked- cation is seen when the eyed Medusae.

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  • A, colony of but grow in all planes Lar;B and C, young and adult medusae.

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  • Whereas primitively any polyp in a colony may produce medusa-buds, in many hydroid colonies medusae are budded only by certain polyps termed blastostyles (fig.

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  • In some species of the genus Cunina (Narcomedusae) the youngest individuals (actinulae) are parasitic on other medusae (see below), but in later life the parasitic From Allman's Gymnoblastic Hydroids, by permission of habit is abandoned.

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  • habit in Hydro medusae.

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  • 23 and 25); and, fourthly, in structure, being hollow or solid, as in the polyp. In some medusae, for instance, the remarkable deep-sea family Pectyllidae, the tentacles may bear suckers, by which the animal may attach itself temporarily.

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  • The sub-umbrella invariably shows a velum as an inwardly projecting ridge or rim at its margin, within the circle .of tentacles; hence the medusae of this sub-class are termed craspedote.

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  • In contrast with the polyp, the longitudinal muscle-system is entirely ectodermal, there being no endodermal muscles in craspedote medusae.

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  • The other, the " lower " or subumbral nerve-ring, is derived from the ectoderm on the sub-umbral side of the velum; it contains fewer but larger ganglion-cells and innervates the muscles of the velum (see diagram in article Medusae).

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  • The sense-organs of medusae are of two kinds - first, organs sensitive to light, usually termed ocelli (fig.

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  • - Muscular Cells of Medusae (Lizzia).

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  • Further, two distinct types of otocyst can be recognized in the Hydro medusae; that of the Leptolinae, in which the entire organ is ectodermal, concrement-cells and all, and the organ is not a tentaculocyst; and that of the Trachylinae, in which the organ is a tentaculocyst, and the concrement-cells are endodermal, derived from the endoderm of the modified tentacle, while the rest of the organ is ectodermal.

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  • - Section of statocyst of Geryonia medusae are the (Carmarina hastata) .

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  • The sense-organs of the two fresh-water medusae Limnocodium and Limnocnida are peculiar and of rather doubtful nature '(see' E.

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  • Moreover, all the medusae budded from a given hydroid colony are either male or female, so that even the non-sexual polyp must be considered to have a latent sex.

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  • It has been shown above that polyps are budded only from polyps and that the medusae may be budded either from polyps or from medusae.

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  • Normally the medusae are liberated in quite an immature state; they swim away, feed, grow and become adult mature el individuals.

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  • - Portions of Sections through will be brought about if the Disk of Medusae - the upper one of the medusae mature Lizzia, the lower of Aurelia.

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  • In some cases both free medusae and gonophores may be produced from the same hydroid colony.

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  • This is the case in Syncoryne mirabilis (Allman [1], p. 278) and in Campanularia volubilis; in the latter, free medusae are produced in summer, gonophores in winter (Duplessis [14]).

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  • Again in Pennaria, the male medusae are set free st.c, Statocyst containing the minute cyst.

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  • in a state of maturity, and have ocelli; the female medusae remain attached and have no sense organs.

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  • As medusae are known to bud medusae from the radial canals there is nothing impossible in Aliman's theory, but it cannot be said to have; received satisfactory proof.

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  • It is convenient to distinguish buds that give rise to polyps from those that form medusae.

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  • Hence the budding of medusae exemplifies very clearly a common phenomenon in development, a phylogenetic series of events completely dislocated in the ontogenetic time-sequence.

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  • and can only be explained on the theory that gonophores are degenerate medusae, and is inexplicable on the opposed view that: medusae are derived from gonophores secondarily set free.

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  • however, both of the statements and figures of Lang and of the facts to be described presently for medusae (Margellium), it is at least theoretically possible that both germinal and vegetative budding may occur in polyps as well as in medusae.

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  • 2 may be produced on the medusa-buds before the latter are set free as medusae.

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  • B, The lower layer forms a solid G,H, Formation of the medusae.

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  • The life-cycle of the Leptolinae consists of an alternation of generations in which non-sexual individuals, polyps, produce by budding sexual individuals, medusae, which give rise by the sexual process to the non-sexual polyps again, so completing the cycle.

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  • Hence the Trachylinae are termed " hypogenetic " medusae to contrast them with the metagenetic Leptolinae.

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  • Thus in Cunina octonaria, the ovum develops into an actinula which buds daughteractinulae; all of them, both parent and offspring, develop into medusae, so that there is no alternation of generations, but only larval multiplication.

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  • In Cunina parasitica, however, the ovum develops into an actinula, which buds actinulae as before, but only the daughter-actinulae develop into medusae, while the original, parent-actinula dies off; here, therefore, larval budding has led to a true alternation of generations.

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  • founder-polyp) nor its offspring by budding (polyps of the colony) have the power of becoming medusae, but only of producing medusae by budding.

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  • For the most part, polyp and medusa have been regarded as modifications of a common type, a view supported by the existence, among Scyphomedusae (q.v.), of sessile polyp-like medusae (Lucernaria, &c.).

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  • Leuckart in 1848 compared medusae in general terms to flattened polyps.

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  • Mechnikov considered the plate thus formed at the base of the polyp as equivalent to the umbrella, and the body of the polyp as equivalent to the manubrium, of the medusa; on this view the marginal tentacles almost invariably present in medusae are new formations, and the tentacles of the polyp are represented in the medusa by the oral arms which may occur round the mouth, and which sometimes, e.g.

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  • Apart from the weighty arguments which the development furnishes against the theories of Allman and Mechnikov, it may be pointed out that neither hypothesis gives a satisfactory explanation of a structure universally present in medusae of whatever class, namely the endoderm-lamella, discovered by the brothers O.

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  • The evidence against this view may be classed under two heads: first, comparative evidence; hydroids very different in their structural characters and widely separate in the systematic classification of these organisms may produce medusae very similar, at least so far as the essential features of medusan organization are concerned; on the other hydroids closely allied, perhaps almost indistinguishable, may produce gonophores in the one case, medusae in the other; for example, Hydractinia (gonophores) and Podocoryne (medusae), Tubularia (gonophores) and Ectopleura (medusae), Coryne (gonophores) and Syncoryne (medusae),-and so on.

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  • Hence it may be concluded that the gonophores are degenerate medusae, and not that the medusae are highly elaborated gonophores, as the organ-theory requires.

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  • - Hydro- medusae with alternation of generations (metagenesis)in which a non-sexual polypgeneration (trophosome) produces by budding a sexual medusa-generation (gonosome).

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  • The polyp usually has the body distinctly divisible into hydranth, hydrocaulus and hydrorhiza, and is usually clothed in a perisarc. The medusae may be set free or may remain attached to the polyp-colony and degenerate into a gonophore.

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  • Thus many subdivisions are diagnosed by setting free medusae in one case, or producing gonophores in another, although it is very obvious, as pointed out above, that a genus producing medusae may be far more closely allied to one producing gonophores than to another producing medusae, or vice versa, and that in some cases the production of medusae or gonophores varies with the season or the sex.

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  • Gonosome with free medusae or gonophores; medusae usually with ocelli, never with otocysts.

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  • In some cases, any polyp of the colony may bud medusae; in other cases, only certain polyps, the blastostyles, have this power.

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  • Until quite recently the hydroids (Gymnoblastea) and the medusae (Anthomedusae) have been classified separately, since the connexion between them was insufficiently known.

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  • Trophosome arborescent, with hydranths of Bougainvillea-type; gonosome free medusae or gonophores, the medusae with solid tentacles in tufts (lophonematous).

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  • 12, 13), and the medusae Hippocrene (budded from Bougainvillea), Margelis, Rathkea (fig.

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  • Trophosome encrusting with hydranths of Bougainvillea-type, polyps differentiated into blastostyles, gastrozoids and dactylozoids; gonosome free medusae or gonophores.

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  • The typical genus is the well-known hydroid Podocoryne, budding the medusa known as Dysmorphosa; Thamnostylus, Cytaeis, &c., are other medusae with unknown hydroids.

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  • Trophosome, polyps with two whorls of tentacles, the lower filiform, the upper capitate; gonosome, free medusae, with tentacles solid and branched.

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  • Trophosome, polyps with a single whorl of capitate tentacles; gonosome, free medusae, with ten tacles branched, solid.

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  • Corymorphidae (including the medusa-family Hybocodonidae).--, Trophosome solitary polyps, with two whorls of tentacles; gonosome, free medusae or gonophores.

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  • Trophosome, polyps with scattered filiform tentacles; gonosome, medusae or gonophores, the medusae with hollow tentacles.

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  • Turris produces free medusae.

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  • - Tropho- some unknown; gonosome, free medusae, with deep, bell-shaped umbrella, with interradial gonads on the base of the stomach, with branched radial canals, and correspondingly numerous hollow tentacles.

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  • gonosome, free medusae or gonoThe apex of the stomach is prophores.

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  • Syncoryne, indistinguishable from it, produces medusae known as Sarsia (fig.

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  • Trophosome (only known in one genus), polyps with two tentacles forming a creeping colony; gonosome, free medusae with four, six or more radial canals, giving off one or more lateral branches which run to the margin of the umbrella, with the stomach produced into four, six or more lobes, upon which the gonads are developed; the mouth with four lips or with a folded margin; the tentacles simple, arranged evenly round the margin of the umbrella.

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  • It buds medusae, which, however, are as yet only known in an immature condition (C. Mereschkowsky [41]).

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  • Doubtful families, or forms difficult to classify, are: Pteronemidae, Medusae of Cladonemid type, with hydroids for the most part unknown.

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  • The medusae, on the other hand, have the tentacles in four tufts of (in the buds) five each, and thus resemble the medusae of the family Margelidae.

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  • Gonosome with free medusae or gonophores; the medusae typically with otocysts, sometimes with cordyli or ocelli (figs.

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  • The gonotheca is formed in its early stage in the same way as the hydrotheca, but the remains of the hydranth persists as an operculum closing the capsule, to be withdrawn when the medusae or genital products are set free (fig.

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  • Numerous medusae are budded successively within the gonotheca and set free; they swim off and mature in the open sea (Allman [1], p. 48, figs.

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  • Medusae, so-called " meconidia," are budded but not liberated; each in turn, when it reaches sexual maturity, is protruded from the gonotheca by elongation of the stalk, and sets free the embryos, after which it withers and is replaced by another (Allman [1], p. 57, fig.

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  • It is quite possible that some of these medusae will be found to be truly hypogenetic, that is to say, with a life-cycle secondarily simplified by suppression of metagenesis.

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  • - Tropho so m e with stalked hydrothecae; gonosome, free medusae with otocysts and four, rarely six or eight, unbranched radial canals.

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  • - Trophosome only known in one genus (Polycanna), and similar to the preceding; gonosome, free medusae with otocysts and with at least eight radial canals, often a hundred or more, simple or branched.

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  • - Trophosome only known in one genus (Thaumantias), similar to that of the Eucopidae; gonosome, free medusae with otocysts inconspicuous or absent, with usually four, sometimes eight, rarely more than eight, radial canals, simple and unbranched, along which the gonads are developed, with numerous tentacles bearing ocelli and with marginal sense-clubs.

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  • - Trophosome unknown; gonosome, free medusae, with four or six radial canals, bearing the gonads, with numerous tentacles, between which occur sense-clubs, without otocysts.

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  • - Trophosome unknown; gonosome, free medusae of deep form, with radial canals branched in a feathery manner, and After Haeckel, System der Medusen, by permission of Gustav Fischer.

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  • - Trophosome as in the preceding; gonosome, free medusae or gonophores, the medusae with large open otocysts.

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  • a section apart, contrasting sharply with the families next to be mentioned, in none of which are free medusae liberated from the colony, so that only the characters of the trophosome need be considered.) 8.

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  • - Metagenetic colony-forming Hydromedusae, in which the polyp-colony forms a massive, calcareous corallum into which the polyps can be retracted; polyp-individuals always of two kinds, gastrozoids and dactylozoids; gonosome either free medusae or sessile gonophores.

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  • (From Moseley.) irregular coenosarcal canals, the coenosteum may contain, in its superficial portion, chambers or ampullae, in which the reproductive zoids (medusae or gonophores) are budded from the coenosarc.

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  • irregular in form; pores scattered irregularly or in cyclosystems, without styles, with transverse tabulae; free medusae.

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  • The gonosome consists of free medusae in Milleporidae, which are budded from the apex of a dactylozoid in Millepora murrayi, but in other species from the coenosarcal canals.

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  • The medusae In such a system the dactylo- 'gastropore, so that the entire single aperture subdivided by FIG.

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  • Medusae with sense-organs represented by otocysts derived from modified tentacles (tentaculocysts), containing otoliths of endodermal origin, and innervated from the ex-umbral nerve-ring.

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  • This order, containing the typical oceanic medusae, is divided into two sub-orders.

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  • The medusae of this order are characterized by the tough, rigid consistence of the umbrella, due partly to the dense nature of the mesogloea, partly to the presence of a marginal rim of chondral tissue, consisting of thickened ectoderm containing great numbers of nematocysts, and forming, as it were, a cushion-tyre supporting the edge of the umbrella.

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  • The actinula, when free, may multiply by larval budding, but in all cases both the original actinula and all its descendants become converted into medusae, so that there is no alter nation of generations.

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  • The buds become medusae by the direct method of budding described above.

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  • Of doubtful position, but commonly referred to the Trachylinae, are the two genera of fresh-water medusae, Limnocodium and Limnocnida.

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  • It is a re markable fact that all specimens of Limnocodium hitherto seen have been males; it may be inferred from this either that only one polypstock has been introduced into Europe, from which all the medusae seen hitherto have been budded, or perhaps that the female medusa is a sessile gonophore, as in Pennaria.

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  • It buds medusae from the margin of the mouth in May and June, and in August and September the gonads' are formed in the place where the buds arose.

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  • Both these medusae have sense-organs of a peculiar type, which are said to contain an endodermal axis like the sense-organs of Trachylinae, but the fact has recently been called in question for FIG.

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  • In this connexion must be mentioned, finally, the medusae budded from the fresh-water polyp Microhydra.

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  • In view of the great resemblance between Microhydra and the polyp of Limnocodium, it might be expected that the medusae to which they give origin would also be similar.

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  • As yet, however, the medusa of Microhydra has only been seen in an immature condition, but it shows some well-marked differences from Limnocodium, especially in the structure of the tentacles, which furnish useful characters for distinguishing species amongst medusae.

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  • A given cormus may bear one or several nectocalyces, and by their contractions they propel the colony slowly along, like so many medusae harnessed together.

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  • Gonostyles, appendages which produce by budding medusae or gonophores, like the blastostyles of a hydroid colony.

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  • In their most primitive form they are seen in Velella as " gonosiphons," which possess mouths like the ordinary sterile siphons and bud free medusae.

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  • They show every transition between free medusae and sporosacs, as already described for hydroid colonies.

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  • Thus in Velella free medusae are produced, which have been described as an independent genus of medusae, Chrysomitra.

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  • In other types the medusae may be set G, Cavity of the large central and a " trachea.

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  • If fertile they become free medusae or sessile gonophores.

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  • Brooks, " The LifeHistory of the Hydromedusae: a discussion of the Origin of the Medusae, and of the significance of Metagenesis," Mem.

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  • Browne, " On British Hydroids and Medusae," Proc. Zool.

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  • " Biscayan Medusae," Trans.

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  • "Medusae " in Herdman, Rep. Pearl Oyster Fisheries, Gulf of Manaar, iv.

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  • " Deep Sea Medusae," in Reports of the Challenger Expedition, Zool.

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  • Hickson, " The Medusae of Millepora," Proc. Roy.

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  • Murbach and C. Shearer, " On Medusae from the Coast of British Columbia and Alaska," Proc. Zool.

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  • Vertebres) also used the term, as when he spoke of the Medusae as radiata medusaria et anomala; but he preferred the term Radiaria, under which he included Echinodermata and Medusae.

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  • But the most striking of the coast-belt flora are the tropical forms - the palm, mangrove, wild banana (Strelitzia augusta), tree-ferns, tree euphorbia, candelabra spurge and Caput medusae.

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  • Wotton follows Aristotle 1 in the division of animals into the Enaema and the Anaema, and in fact in the recognition of all the groups above given, adding only one large group to those recognized by Aristotle under the Anaema, modifica- namely, the group of Zoophyta, in which Wotton includes the Holothuriae, Star-Fishes, Medusae, Sea-Anemones and Sponges.

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  • We find that polyps may either bud other polyps or may produce medusae, and that medusae may bud medusae, though never, apparently, polyps.

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  • Hence we have a primary subdivision of the colonies of Hydrozoa into those produced by budding of polyps and those produced by budding of medusae.

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  • Medusae capture their prey, consisting of small organisms of various kinds, especially Crustacea, by means of the tentacles which hang out like fishing-lines in all directions.

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  • Medusae thus form an important constituent of the plankton or floating fauna of the ocean, and compete with fish and other animals for the food-supply furnished by minuter forms of life.

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  • divisions of the medusae are characterized by the presence or absence of a velum.

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  • Every possible variety of body-form compatible with the foregoing description may be exhibited by different species of medusae.

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  • (For other figures of medusae see Hydrozoa.) of the mouth.

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  • The sense-organs of medusae are of two classes: (1) pigment spots, sensitive to light, termed ocelli, which may become elaborated into eye-like structures with lens, retina and vitreous body; (2) organs of the sense of balance or orientation, commonly termed otocysts or statocysts.

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  • (For fuller information upon the sense-organs see Hydromedusae.) Medusae are nearly always of separate sexes, and instances of hermaphroditism are rare.

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  • Medusae often have the power of budding, and the buds are formed either on the manubrium, or at the margin of the umbrella, or on an outgrowth or "stolon" produced from the exumbral surface.

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  • Medusae, when they reproduce themselves by budding, always produce medusae, but when they reproduce by the sexual method the embryos produced from the egg grow into medusae in some cases, in other cases into polyps which bud medusae in their turn.

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  • Medusae are exclusively aquatic animals and for the most part marine, but at least two fresh-water species are known.'

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  • A parasitic mode of life is also seen in medusae of the genus Cunina during the larval condition, but the habit is abandoned, in this case, when the medusae become adult.

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  • For figures of medusae see (i) E.

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  • Jena (1879, 2 vols.); (2) Id., "Deep-Sea Medusae," Challenger Reports, Zoology, IV.

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  • The Mollusca agree in being coelomate with the phyla Vertebrata, Platyhelmia (flat-worms), Echinoderma, Appendiculata (insects, ringed-worms, &c.), and others - in fact, with all the Metazoa except the sponges, corals, polyps, and medusae.

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  • When beetles, or medusae, or cats vary, the range of possible variation is limited and determined by the beetle, medusa or cat constitution, and any possible further differentiation or specialization must be in a sense at least orthogenetic - that is to say, a continuation of the line along which the ancestors of the individual in question have been forced.

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