4 
Transactions of the 
remain in its place and take part in the building up of the small 
blood-vessels, or be thrown off from its mother-body and be developed 
into a nucleus itself. In the latter case its contents become more 
opaque and small granules appear within them. 
The concave depression which the young nucleus leaves behind 
on the surface of the mother-nucleus never disappears entirely, no 
matter how much the latter may change its original form by the 
production of others. For this reason the productive force of the 
mother-body can always be inferred from the number of depressions. 
Several vesicles or young nuclei may arise simultaneously from the 
old one (Fig. 3) ; accordingly, I observed in the chorion of the 
ovum in question a number of them, bearing three to four vesicles, 
and, judging by the number of depressions, one nucleus may even 
produce five to six of its kind. Along with the production of new 
vesicles the substance of the old nucleus seems to be rendered more 
dense, its double contour and the granules it contains become less 
distinct, and the whole body assumes at last a shining, greenish tint. 
This is especially the case in specimens which have been laying for 
a few days in a weak solution of chromic acid ; in these, the vesicle, 
at its first appearance, is distinguished by a reddish tint. In con- 
sequence of the concave depressions, produced by the formation of 
the vesicles, and in proportion to the diameter of the latter, the 
mother-nuclei appear in many fold, mostly unsymmetrical forms 
(Figs. 3, 4, and 5), and it is difficult to find an object of suitable 
comparison. In many cases the vesicle is developed, as in the 
formation of blood-vessels, into a large, clear, double-contoured cell. 
The greater now the diameter of the cell, the greater is also the 
depression observed on the nucleus, and it is for this reason that, 
after the production of a number of cells, very little of the substance 
of the nucleus is left. Equally as varying as the form of these 
nuclei were their diameters; while, namely, those of the smaller 
ones only reach to about xw mm., those of the larger attain a size 
of about T tlo mm. in length, by T J o mm. in breadth. The latter are 
found in connection with the formation of the first embryonic blood- 
vessels. The more the entire embryo advances in its development, 
the more also the size and fertility of these mother-nuclei are 
reduced. 
Long before I discovered these mother-nuclei, bearing buds in 
the form of cells, in the membranes of the ovum, I had met with 
them in the nervous tissues as well as in the pia mater of those 
human embryos on which I had worked. But as they appeared 
here in a smaller form, and with smaller vesicles or corresponding 
depressions, I failed to recognize their true nature, and considered 
them passingly as old nuclei, deformed by degeneration. Never- 
theless, however, did I observe in their immediate neighbourhood, 
their offsprings in the form of small, round, and pale bodies, which, 
