THE OVUM AND
the internal surface of it. Three is the largest number of nucleoli which I have observed in other nuclei, and Schleiden has in some very rare instances seen four in plants. If, however, they are only the contents of the nucleus, and not nucleoli, it must be allowed that they differ very much from the contents of almost all other nuclei, which are generally yellowish, and made up of extremely minute granules. The only exception which I have met with was that already mentioned respecting the nucleus of the adipose cells in the cranial cavity of a young carp. This last point seems therefore rather in favour of the germ-vesicle being regarded as a young cell. [1]
When the whole of the above detailed evidence is reflected upon in connexion, it will be seen that it is as yet impossible to decide the question as to whether the germinal vesicle be cell or nucleus. The opinion that the vesicle is to be regarded as a cell-nucleus, seems for the present to have the ascendancy, inasmuch as the observations upon the first and most important point, viz. the prior existence of the germ-vesicle to that of the yelk-cell appear to be in favour of that view. [2] The sub-
- ↑ Since in vegetable cells the nucleolus is the primary formation, and the nucleus a secondary one around it, and as the same has been shown to be most probably the case in animal cells, (see page 20, on the production of the nucleus of cartilage-cells,) so also in this case the signification to be assigned to Wagner’s spot depends upon the history of the development of the germ-vesicle. The observations of Wagner, quoted in the Supplement, show, however, that the single germinal spot of the ova of insects is first formed, and the germinal vesicle afterwards around it. The former must then be considered as nucleolus to the vesicle, which correspondsto the nucleus. When several of Wagner’s spots occur, their signification is totally different from that of the first one, and they are to be regarded only as secondary formations in the interior of the germ-vesicle. In fact, the younger the ova of fishes and frogs, the fewer spots are observed in them.
- ↑ The following is the probable course of formation of the ovum, according to the researches now before us; the ovisac (Eisach, ovisac of Barry, internal membrane of the Graafian vesicle) is first developed. In this (according to analogy with Wagner’s observations on the ova of insects) a germinal spot is generated, asnucleolus to the ovum. Around that spot the germinal vesicle is formed as nucleus to the ovum; and round this again the ovum-cell (Eizelle.) Martin Barry, indeed, (1. c. p. 308,) conjectures that the germ-vesicle is formed previously to the ovisac; but my respected friend expresses himself with great caution on the ques- tion; and it would in fact be difficult to determine whether a given vesicle were a germinal vesicle, around which no ovisac had as yet formed, or an ovisac within which no germ-vesicle had as yet formed. The occurrence also in the lower ani-
