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.

    132/482 (page 128)
    The few observations hitherto made upon the genital organs of the Gor- diacei have shown that they are wholly tubular as in the Nematodes. But their intimate structure, and the development of their spermatic particles are so strikingly different, that this point alone would justify their separ- ation from the Nematodes.(10) § H8. With the exception of the Nematodes, and Gordiacei, the development of all Helminthes, which reproduce by means of genital organs and eggs, is metamorphotic. A complete series, from beginning to end of these meta- morphoses has yet never been observed with any species. From the separate parts of it here and there which have been observed, there appears the remarkable fact, that the embryos after escaping the egg, are not always changed at the end of the metamorphosis, into individuals like the parent, but appear as larva-like animals, capable in their turn of producing other larvae. These last larvae alone, change into individuals, which are like the parent. This particular kind of transformation and development which is quite common among the Trematodes, has received the name of Alternate Gene- ration.(1) Whether it occurs among the Cestodes and Acanthocephali, cannot now be stated positively, for as yet we are unacquainted with the first period of their metamorphosis, — the embryo as it escapes from the egg.(2) In many Cestodes and Trematodes, the embryos are developed before the eggs are cast, and in some of the last order, they make their escape while the eggs are in the uterus. The development of the Cestodes occurs as follows: After the disap- pearance of the germinative vesicle, large, transparent embryonic cells appear in the midst of the vitellus, which undergoes fissuration. These multiply by division, increasing at the expense of the vitellus, which in the tightly to the vulva of the female in this act, that they cannot disengage themselves (Siebold and Nathusius, in Wiegmann's Arch. 1836,1. p. 105, Taf. III. 1837, I. p. 60, 66). With many other species of Strongylus, and Ascaris, it is not rare to find a brownish gum about the vulva, and in which there is, sometimes, the very distinct impress of the male caudal valve (.Mehlis, Isis, 1831, p. 87).* 10 In the genus Mermis formed by Dujardin, the tubular uterus, the muscular vagina, and the vulva situated far from the caudal extremity, — all remind one much of the Nematodes. The eggs of Mermis nigrescens, like those of Ascaris den- tata, have long fibrillated appendages (Dujardin Ann. d. Sc. Nat. 1842, XVIII. p. 133, PI. VI., and Siebold, in Wiegmann's Arch. 1843, II. p. 309) $ and at the caudal extremity of the males of Mermis albicans, mihi (Entom. Zeit. 1843, p. 79), there are, as in most Nematodes, two horny penises. But with Gordius, the structure of the genital organs is very different (see Siebold, and Dujar- din, loc. cit.). In both sexes the cavity of the body is completely filled with a double genital tube, straight, and simple posteriorly, the sides of which aie formed of large cells. The genital * [ § 117, note 9.] For many details of the re- productive organs of Ascaris infecta, with beauti- ful illustrative figures, see Leidy, A Flora and Fauna, &c., loc. cit. 4 B. PI. VII. 14,16, b. 19.— Ed. t [ § 118, note 2.] The view here suggested of opening is always at the posterior extremity of the body. The testicular tubes of Gordius aquations .contain anteriorly, cell-like bodies ; but posteriorly there are others, staff-like, and which, being found among the eggs in the uterine tube, I have regarded as perfect spermatic particles. The genital open- ing of the male Gordius is between the two more or less prominent lobes of the caudal extremity, and is without copulatory organs. The simple, round, colorless eggs, are bound together at the posterior part of the uterus by an albuminous sub- stance, and are deposited in a very long row. It is this row of eggs which Lion Dufour has described as Filaria Jilariae (Ann. d. Sc. Nat. XIV. 1828, p. 222, PL XII. fig. 4). 1 See Steenstrup, Ueber den Generationswech- sel, &c., 1842. v In various marine fish there is a trematode larva of a Tetrarhynchus (Miescher, Bericut ueber die Verhandl. d. Naturforsch. Gesellsch. in Basel. 1840, p. 29, and in Wiegmann1 s Arch 1841, II. p. 302), which would lead one to con- clude that alternate generation exists also with the Cestodes.t , the alternating generation of the Cestodes, has recently been confirmed most thoroughly by Sie- bold, who has treated the subject in a most com- prehensive manner, in a Memoir in Siebold and Kblli/ceFs Zeitsch. II. 1850, p. 198. — Ed.