282 MR. F. E. BEDDARD ON THE [May 4, 



very dissimilar to true nuclei, and the sphere has no limiting mem- 

 brane. It is doubtful therefore whether they can be regarded as 

 cells, though it is probable that, as the segmentation of the ovum 

 advances, the white yolk is directly converted into cells. Now in 

 the cell-like bodies vvhich I have described in the immature ovum of 

 Lepidosiren there is a very distinct and obvious nucleus (figs. 9-20), 

 which is in fact entirely similar to a nucleus of one of the follicular 

 cells ; it is deeply stained by borax carmine and unevenly stained, 

 so that it has the appearance of being formed of a raeshwork of 

 condensed protoplasm, the interspaces of which are filled by a 

 homogeneous substance which is less acted upon by the reagent. 

 In some instances there was more than a single nucleus to each of 

 these cells, but it is quite impossible to confound these nuclei with 

 the surrounding particles of yolk. Furthermore, in many cases the 

 limiting membrane of the cells was distinctly visible (figs. 9 &c.) ; 

 and the fact that the cell-contents were hardly acted upon by the 

 staining fluid rendered the perception of this membrane easier. 

 There seems to be but Uttle doubt that these structures are veritable 

 cells, and are not in any way comparable to the white yolk-spheres. 

 The question then arise's, What is the origin of these cells ? Are they 

 formed anew within the substance of the ovum, or have they migrated 

 from the follicle into the interior of the ovum ? 



The former supposition is supported by no facts that I have been 

 able to note, and it is distinctly negatived by other facts. 



In the first place, these cells are very closely similar to the cells 

 of the follicular epitheUum ; like them they are bounded by a 

 distinct limiting membrane ; the contents of both consist of proto- 

 plasmic strands and numerous highly refractive particles similar to 

 the yolk-particles ; the nucleus is identical in shape and size ; and 

 the behaviour of both to the staining reagent is precisely the same. 

 This series of facts would, however, be hardly regarded as proof that 

 these cells have originated from the follicular epithelium ; it might 

 be supposed that the cells have arisen within the ovum, and that 

 some of them have migrated to the periphery to form the follicle, as 

 has been stated by various observers to be the case in certain other 

 ova (see p. 276) ; but the immense vascular development round 

 the follicular epithelium that has been already mentioned seems to 

 indicate that the main activity is centered in these latter cells ; and 

 this fact, coupled with the additional fact that in certain instances 

 there were masses of migrating cells evidently in course of being 

 budded oif (Plate XXVIII. figs. 5, 6) from the follicular epithelium, 

 seems to indicate that the second supposition as to the origin of these 

 cells is correct, viz. that they are formed by the proliferation of the 

 follicular cells and migrate into the interior of the ovary. 



The migration of these cells also explains the absence of a limiting 

 membrane to the ovum. A "formed" membrane, however thin, 

 would evidently prevent such a migration. 



It appears to me possible to make another statement as a deduction 

 from the facts just detailed : that the follicular epitheliuni-cells 

 secrete the yolk which is conveyed to the interior of the ovum hy 



