Comparative anatomy / by C.Th. v. Siebold and H. Stannius ; translated from the German, and edited with notes and additions recording the recent progress of the science by Waldo I. Burnett.

  • Karl Theodor Ernst von Siebold
Date:
1854
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Licence: Public Domain Mark

Credit: Comparative anatomy / by C.Th. v. Siebold and H. Stannius ; translated from the German, and edited with notes and additions recording the recent progress of the science by Waldo I. Burnett. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    of procreation, the females of some Discophora are easily distinguished from the males by the numerous pouches of their tentacles, and in which eggs and newly-hatched young are carried for a short time.*121 §70. As yet, the development of a few only of the Acalephae has been traced. It is attended by a remarkable metamorphosis. After the usual segmentation of the vitellus, ovoid embryos resembling infusoria are developed; these turn freely on their axis, and swim about in the water by means of ciliated epithelium.(1) Shortly after, they become attached by the anterior extremity to some object. Upon the opposite free extremity tentacles appear, and between them the mouth. The animal has then the form of a Polyp.(2) It is during this period that the young ani- mal reproduces by gemmation,(3) and sometimes by transverse fissuration. This last mode occurs in the following remarkable manner: The polyp-like animal increases in length, and its body divides trans- versely into many segments. Around each of these segments eight bifid processes are developed; after this, each segment is successively separated from before to behind, and they float about for a time as eight-rayed Aca- lephae, but soon attain, however, their adult condition.<4J seen genital organs of the same form between the tentacles of Agalmopsis ; but he found at the same time (loc. cit. p. 38,43), in the campanuliform individ- uals produced from buds, testicles with Agalmopsis, and ovaries with Diphyes. It may therefore be justly supposed that these various Siphonophora are compound, sexless individuals, which, like the Hydrina and Sertularina, reproduce by alternation of generation, — that is, by buds, — individuals having sex. 1 '2 Medusa aurita and Cyanea capillata; see Ehrenberg, Abhanal. &c. loc. cit. Taf. III. fig. 1, 2, Taf. VIII. fig. 1 *, also, Sars in Wiegmann's Arch. 1841, I. p. 19. 1 The development and metamorphosis of Me- dusa aurita and of Cyanea capillata have been observed by Siebold (BeitrSge loc. cit. p. 21, Taf. I. II. *, and Froriep's neue Not. No. 166, 1838, p. 177) ; and by Sars (Wiegmann’s Arch. 1841,1. p. 19, Taft I.-IV.). In the first stage of development (see Ehrenberg, Abhandl. &c. loc. cit. Taf. VIII. fig. 15-18 5 also, Siebold, Beitrage loc. cit. Taf. I. fig. 17-19 ; and Sars, Wiegmann's Arch. loc. cit. Taf. I. fig. 1-6), these infusoria-like Medusae have been regarded by Baer as the larvas (MeckeVs Deutsches Arch. VIII. 1823, p. 389). 2 Siebold, Beitrage loc. cit. p. 29, Taf. I. fig. 25^-33, Taf. II. fig. 34; and Sars, Wiegmann’s Arch. loc. cit. Taf. I. fig. 7-31. During my last visit at Trieste (autumn of 1847), I convinced myself that the young of Cephea Wagneri are developed wholly like those of Medusae, by passing from infusoria-like forms to polypoid young ani- mals.* 8 The reproduction of the polyp-form Medusae by buds has been observed by Sars in Cyanea * [ § 70, note 2.] See, also, for recent researches on the development of Cephea, Ecker, Bericht iib. die Verhandl. d. naturf. Gesellsch. in Basel. VIII. 1849, p. 51 *, Busch, Beobachtungen iib. die Anat. &c. Berlin, 1851, p. 30 ; and Frantzius, in Sie- capillata. He has also seen them develop pedi- cles from the end of which new individuals would appear, which resembled Polyps. See Wiegmann’s Arch. loc. cit. p. 26, Taf. I. fig. 37, 41, 42, 38, 39, 40. 4 These young Medusae, whilst composed of rings, have been taken for a new genus (Scyphistoma) of Polyps by Sars (Isis. 1833, p. 222, Taf. X. fig. 2). Steenstrup (Ueber d. Generationswechsel, p. 17) has regarded them as nurses of the Medusae. At a latter period, when the rings have been separated and have acquired the bifid prolongations, Sars (Isis. 1833, p. 224, Taf. X. fig. 4 ; and Beskrivel- ser, &c., p. 16, PI. III.) has described them as a new species of Medusae (Strobila octoradiata). But lately he has perceived that they are the young of Medusa aurita (Wiegmanri's Arch. 1837, I. p. 406); it did not occur to him, however, that these young constitute, very probably, the genus Ephyra of Eschscholtz (see Wiegmann’s Arch. 1841, Th. I. p. 10). It will probably be discovered that many small campanulate or discoid Medusae are only the young of other Acalephae; for it is very likely that they all undergo a similar metamorpho- sis. It may also prove that many naked Polyps are only transitionary forms of known species of Acalephae. In this connection the observation of Dujardin (Comp. rend. 1843, p. 1132) deserves the attention of naturalists. In tracing the devel- opment of one of the Discophora allied to Oceania, he observed that this animal in its early condition separated from a corallum resembling that of Syn- coryne, and was of a form quite like an Eleuthe- ria. However various these developing forms may be, that one must be regarded as the real one wliich exists during the development of the testi- cles and ovaries.t bold and Kblliker's Zeitsch. f. Zool. IV. p. 118, June, 1852. — Ed. f [ § 70, note 4.] In regard to the development of the Acalephae, it may be mentioned that recent researches, few as they are, have verified some