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 un- 

 wittingly ignored the contents of a paper by H. Ludwig', 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 mem- 

 brane, and break away to form an ovum, which is, according to 

 Huxley , never fertilized but develops partlienogenetically , It is 

 true that the statement about the non-fertilization of these ova has 

 been questioned by a later observer^ but much weight must obvi- 

 ously 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', se- 

 condary follicle-layer ; bl, blood-vessels ; c, central cells ; m, 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 stronia- 



cell ; h, follicular layer ; d, central cells. 



4. Lymph-cells (?) from multicellular body of Protojjterus. 



5. Nuclei of germinal cells from secondary follicle-layer of body, illus- 



trated in fig. 1. a, a nucleus from one of the same cells on the side 

 of the body opposite to the area of invagination. 



Plate LIII. 

 Fig. 6. Transverse section through a portion of outer surface of multicellular 



' Arbeit, a. d. Zool.-zoot. Inst. Wiirzburg, Bd. i. 

 " See Cohn, Zeitschr. f. wiss. Zool. Bd. vii. (1856). 



