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
Catalogue details

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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    same individual during the time of heat both ovaries and testicles are de- veloped upon the external surface of the body. In the place where the eggs are to appear,(1> the transparent and color- less skin rises in the form of swellings, under which the vitelline mass gradually forms. These end each in the form of an excrescence, which, being constricted at its base and rounded, has the shape of an egg. At the point of constriction there is formed from the body of the Polyp a kind of cupel, in the cavity of which the vitellus rests by a small portion of its surface; at this point the skin becomes thin, and ultimately appears like an arachnoid membrane enveloping the egg. In this last neither a germinative vesicle nor dot has been discovered. Its separation is preceded by a thinning of its surrounding membrane, after which the vitellus is im- mediately clothed by a gelatinous substance. In Hydra vulgaris its whole circumference is covered by obtuse prolongations of this kind, which, after an increase in length, divide, each once or more, at their extremity, and so present a dentated appearance. The arachnoid membrane finally bursting, the detached egg becomes fixed to some body, whilst the gelatinous coat entirely disappears. This is equally true of Hydra viridis, with the exception that here the vitelline prolongations are very short and compact.® In these same individuals testicles are developed also. Between the base of the tentacles and the place of the appearance of the egg, there are developed small conical prominences, on the apex of which is a papil- la. This has an orifice which leads into an internal cellular cavity. This is the real testicle, wherein are found spermatic particles composed of a body, or head, to which is attached a very movable tail. These particles easily escape through the orifice, and circulate in the water surrounding the Polyps filled with eggs.® The number of these testicles in a single individual is not definite.(4) * 1 In the arra-polyps, gemmation always pre- cedes propagation by eggs. 2 The eggs of Hydra were long ago observed by Bernhard Jussieu (Abhandl. d. schwed. Akad. 1746, VIII. p. 211). But afterwards they were regarded as exanthemata of this animal (see Roe- sel? Insektenbelust. Th.III. p. 500, Taf. LXXXIII. fig. 1, 2). Their true nature was lately first pointed out by Ehrenberg (Abhandl. d. Berliner Akad. 1336, p. 115, Taf. II.). 3 The testicles of Hydra were known to the elder naturalists, but were taken for an eruptive disease (Trembley Abhandl. zur Geschicht. einer Polype- nart, p. 264, Taf. X. fig. 4, and Roesel, loc. cit. p. 602, Taf. LXXXIII. fig. 4). Latterly this same error has been continued (Laurent in Froriep's neuen Notizen, 1842, No. 513, p. 104). To Ehren- berg is due the first description of their true nature (Mettheil. aus den Verhandl. d. Gesellsch. naturf. Freunde in Berlin, 1838, p. 14). * [At end of § 50.] The so-called ova, mentioned above in the text, may be justly questioned as be- ing true ova, for we know of no real ova which do not contain a germinative vesicle. Then, again, simple oval masses of cells as they are, they would exactly resemble the bud-like eggs of Aphides, and the “ hibernating eggs ” of Daplinia and some of the Rotatoria, all of which are properly gemmae, and do not require the agency of the spermatic 4 Wagner, leones zoot. Tab. XXXIV. fig. 10, b, b. In Hydra vulgaris I have counted fifteen testicles 5 another individual had seven eggs and eleven testicles j and a third, four eggs and twelve testicles. [Additional note to § 50.] Other examples of Anthozoa having external genital organs in the form of egg or sperm capsules have been observed by Van Beneden (Rech. sur l’embryog. d Tubul. pi. V. VI.), Rathlcd (Wiegmann's Arch. 1844, I. Taf. V.), and Sars (Faun, littoral. Norveg. p. 7, Tab. II.), with IJydractinia, Coryne and Podo- coryne. See also the facts collected by Frey and Leuckart (Beitr. &c. p. 28). These egg or sperm capsules may, moreover, be regarded as imperfect male or female individuals, and then the porters of these capsules may be considered, being sexless individuals like those mentioned in § 45, in the category of nurse-like generations which, af- ter a more or less complete development, produce generations with sex. particles for their development. It is also worthy of remark, in this connection, that these ova sprout from the same part of the body in which eggs are developed. Thomson, however (Edinb. New Philos. Jour. 1847, p. 287), speaks of having ob- served the granular mass contained within these so-called eggs divide and subdivide like a proper vitellus, and this while still within the capsule, and attached to the parent animal. This doe3 not