1886. | OVUM OF LEPIDOSIREN. 285 
much like that of the white yolk-spheres of Sauropsida. In any 
case these bodies are not supposed to have an extrinsic origin, but 
to arise within the ovum. On the other hand, a penetration of 
follicular cells through the micropyle (oc. cit. pl. i. fig. 6) appears 
really to occur in many osseous fish and to be comparable to the proli- 
feration into the ovum of the follicular cells in Lepidosiren. 
Kolessnikow’ confirms the accuracy of His’s results as to the 
entrance of leucocytes into the ovum, but does not think this 
process to have much functional importance. 
In Mammals a number of observations have been published which 
tend to show that there is a migration of cells, which is evi- 
dently comparable to the facts which I have detailed above in 
Lepidosiren. Lindgren? has described such a migration of follicular 
cells, and figures an ovum which is half filled with unaltered follicular 
cells. Von Sehlen* and H. Virchow * have confirmed the accuracy 
of Lindgren’s observations. More recently Schater® has described a 
remarkable series of changes in the Rabbit’s ovum which do not 
altogether tend to the same conclusion. In young ova, which are 
as yet surrounded by a follicle consisting of only a single layer of 
cells, peculiar cells make their appearance in the peripheral regions, 
and ultimately form a single layer of cells which surround the ovum, 
lying beneath the follicular layer. Schafer believes that these cells 
are not derived from the follicular layer, but they originate in the 
ovum. He compares very justly his own observations with those 
of Kuppfer on Ascidia canina. Kuppfer® had shown that cells appear 
in the interior of the ovum and range themselves round its periphery. 
Kuppfer, however, believed that these cells originate in the ovum 
itself, and are not, as Kowalevsky supposed, a product of the follicular 
epithelium. His statements therefore are in complete accord with 
those of Scliifer; while Lindgren, von Sehlen, and H. Virchow 
describe a process in the maturation of the mammalian ovum 
which is more comparable to that described by Kowalevsky in the 
case of the Ascidians. ‘The latest writer on the mammalian ovum, 
Mr. Heape, did not find any such migration of follicular cells, and 
concludes that the observations put on record by Lindgren, von 
Sehlen, and Virchow are based upon abnormal processes. It is to 
be noted, however, that the type studied by Heape’ (Mole) was not 
studied by any one of these naturalists, and this fact may possibly 
account for the discrepancies in their statements. In the latest 
edition of Quain’s ‘Anatomy’ it is suggested that the entrance of 
follicular cells into the ovum described by Lindgren, von Sehlen, 
and H. Virchow may be an abnormal process and not a regular 
1 Archiv f. mikr. Anat. vol. xv. (1878) p. 399. 
2 Arch. f. Anat. u. Phys. 1877. 
3 Arch. f. Anat. u. Phys. 1882. 
4 Arch. f. mikr. Anat. Bd. xxiv. (1884). 
5 Proc. Roy. Soe. vol. xxx. (1880) p. 243. 
® Arch. f. mikr. Anat. Bd. viii. See also the papers of many others (Sabatier, 
Roule, Fol) on the Ascidian ovum, and the facts referred to in footnote on 
p. 276, supra. These have been lately summed up in Quart. Journ. Micr. Sci., 
June 188¢, by Mr. Arthur Thomson. 
_ 7 Quart. Journ. Mier. Sci., Feb. 1886. 
