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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    tween the feet of many Branchiati, serve for the escape of the sperm and eggs.(4) With others, the cavity of the body opens outwardly, probably by a loss of the last segment, especially with those which are viviparous.® The water is undoubtedly the medium of fecundation, and receives the sperm from the males, probably through orifices like those which serve for the escape of eggs with the female. With the viviparous Branchiati, water filled with sperm can enter the body and fecundate the eggs through these same openings. §169. The development of the Annelides as far as yet known, occui’S after two different types; but it always commences with a complete segmentation of the vitellus. I. With the Hirudinei, after the vitellus has divided into many large cells, a central one becomes distinguished from the others by its still further division ; this becomes the digestive tube. The others, still dividing, form a primitive embryonic part in which appears the future ventral and nervous portion. The embryo is at first spherical, and ultimately is covered with a delicate ciliary epithelium. A kind of sucker is then developed upon a certain point of its surface; this connects with the stomach, and through it is re- ceived, for food, the albumen surrounding the embryo. It then gradually lengthens, and, losing its ciliary epithelium before the escape from the egg, a sucker appears upon the posterior extremity, and it finally becomes fully developed without a Metamorphosis.® II. With the Branchiati, there is a complete metamorphosis. The seg- mentation of the vitellus is uniform throughout, and this last is finally changed into a round embryo — which, escaping from the egg, swims freely about like an Infusorium, by means of the ciliated epithelium which covers its whole body. The embryo then lengthens, and the epithelium disappears 4 According to Milne Edwards’ observations upon several Capitibranchiati, as Terebella, Ser- pula, Protula, &c., the eggs are glued together in masses by an albuminous substance, and attached to the stones of the anterior border of their cases ; see Ann. d. Sc. Nat. III. 1845, p. 143,161, PI. V. fig. 1, PI. VII. fig. 23, PI. IX. tig. 42. With Poly- nog cirrata, on the other hand, masses of eggs are attached and borne about on the scales of their body ; see Sars, in Wiegmann’s Arch. 1845, I. p. 13, Taf. I. fig. 12. With the females of Exogone and Cystonereis, the eggs are situated in longi- tudinal rows upon the ventral surface *, see Orsted, in Wiegmann's Arch. 1845, I. p. 21, Taf. II. fig. 4, and Kolliker, in an as yet unpublished memoir for the Helvetic Society, titled : Einige Worte zur Entwickelungsgeschichte von Eunice, von H. Koch in Trieste, mit einem Nachwort von Kolliker. [Additional note.] The often-quoted memoir of Koch and Kolliker on the development of the An- * [§ 168, note 4.] According to Felix Dujar- din (Ann. d. Sc. Nat. XV. 1851, p. 298) Exogone pusilla is androgynous. Beside the well-known pediculated ovarian sacs on the ventral surface, each segment of the body, except the first two, ha3, with this species, a dorsal, fusiform cirrus, in which are developed spermatic particles. This ob- nelides has recently appeared in the Neue Schweiz. Denkschr. VIII.* 5 According to my friend H. Koch of Trieste (in the MS. just indicated), the eggs of a species allied to Eunice sanguinea, are developed in the cavity of the female body, whence the young escape through a rupture of its posterior extremity. 1 See F. de Filippi, Lettera sopra l’Anatomia, e lo sviluppo delle Clepsine, Pavia, 183'J, Tav. II. y Grube, Untersuch. fiber die Entwick. d. Clepsine, p. 15, Taf. I., and Frey, Zur Entwickel. von. Nephe- lis vulgaris, in Froriep's neue Not. No. 807, 1846, p. 228. The old observations of E. II. We- ber (Meckel's Arch. 1828, p. 366, Taf. X. XI.; and R. Wagner (Isis, 1832, p. 398, Taf. IV.) agree very well with those of Filippi As yet, we possess nothing upon the develop- ment of Lumbricini, whose young, as is known, like those of the Hirudinei, leave their cocoons without undergoing any metamorphosis.! servation, from its singularity, requires confirm- ation. — Ed. t [ § 169, note 1 ] For the embryology of Ne- mertes, see Desor, Boston Jour. Nat. Hist. VI. p. 1. The general facts accord with those mentioned in the text. —Ed.