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Show 526 MR. F. E. BEDDARD ON THE OVUM IN DIPNOI. [Dec. 7, erroneously stated that there had been no confirmation or refutation of the truth of his discoveries; I find, however, that I have unwittingly ignored the contents of a paper by H . Ludwig1, in which there are described a series of important investigations of the ovary of Apus. Ludwig finds that there is nothing abnormal in the formation of the ova, and that a number of them do not coalesce as stated by v. Siebold ; at least there is no real fusion of the ova, only an accidental running together of the contents of several acini due to ruptures. Ludwig's account is so circumstantial, that there can be no reasonable doubt that the ova of Apus are not formed by the concrescence of several cells. The only other instance that I am acquainted with in which the ovum has been stated to arise from the fusion of a number of cells is in the Rotifer Lacinularia. A curiously similar mode of development of the ovum has been recorded by Huxley in Lacinularia. A number of cells of the ovary become compacted together, enclosed in a common membrane, and break away to form an ovum, which is, according to Huxley , never fertilized but develops parthenogenetically. It is true that the statement about the non-fertilization of these ova has been questioned by a later observer2, but much weight must obviously be given to the observations of the discoverer of the formation of the ' winter ova' in Lacinularia. The mode of origin of these ova is closely parallel to that which I have described above in Protopterus and Ceratodus. The ovary in the Rotifer consists of a mass of cells, some of which develop into ova, and all of which are comparable of course to the germinal cells in the ovary of the Vertebrate. The fusion of a number of these to form a single ovum is therefore clearly analogous to the fusion of a number of germinal cells in Protopterus and Ceratodus. EXPLANATION OF THE PLATES. PLATE LII. Fig. 1. Multicellular body in ovary of Protopterus, Stage I. g.e, germinal epithelium on surface of ovary; f.e, follicular epithelium; f.e', secondary follicle-layer ; bl, blood-vessels ; c, central cells; n, nuclei of central cells; p, mass formed by the fusion of the cell-protoplasm of central cells. 2. A portion of an adult ovum of Ceratodus in which the egg-membranes have disappeared prior to degeneration of ovum, a, stroma-layer ; f.e, follicular layer; y, yolk-spherules. 3. Nest of germinal cells in ovary of Ceratodus. a, nucleus of stroiua-cell; b, follicular layer ; d, central cells. 4. Lymph-cells (?) from multicellular body of Protopterus. 5. Nuclei of germinal cells from secondary follicle-layer of body, illustrated in fig. 1. a, a nucleus from one of the same cells on the side of tbe body opposite to the area of invagination. P L A T E LIII. Fig. 6. Transverse section through a portion of outer surface of multicellular 1 Arbeit, a. d. Zool.-zoot. Inst. Wurzburg, Bd. i. 3 See Cohn, Zeitsehr. f. wiss. Zool. Bd. vii. (1856). |