Page:Proceedings of the Royal Society of London Vol 4.djvu/248

Rh to the pendulum through some principle perfect in itself, and not dependent for its success on superior execution. In the escapement invented by him, the pendulum merely raises a weight, and is im- pelled by that weight through an increased space in its descent. It neither unlocks a detent, nor has anything to do with the train ; and as the weight raised, and the spaces described, are constant quantities, this escapement is, in the strict meaning of the term, one of equal impulse.

John Auldjo, Esq., and William Sharp, Esq, were balloted for, and duly elected into the Society.

A paper was read, entitled " Researches in Embryology, Third Series : a Contribution to the Physiology of Cells." By Martin Barry, M.D., F.R.S., F.R.S.E., Fellow of the Royal CoUege of Physicians in Edinburgh.

In the second series of these researches, the author had traced certain changes in the mammiferous ovum consequent on fecunda- tion. The object of his present communication is to describe their further appearances obtained by the application of higher magnify- ing powers ; and to make known a remarkable process of develop- ment thus discovered. In order to obtain more exact results, his observations were still made on the same animal as before, namely, the rabbit, in the expectation that, if his labours were success- ful, it would be comparatively easy to trace the changes in other mammals. By pursuing the method of obtaining and pre- serving ova from the Fallopian tube which he recommended in his last paper, he has been enabled to find and examine 137 more of these delicate objects ; and has thus had ample opportunity of con- firming the principal facts therein stated. He has now procured in all 230 ova from the Fallopian tube. But being aware that repeated observations alone do not suffice in researches of this nature, unless extended to the very earliest stages, he again specially directed his attention to the ovum while it is still within the ovary, with a view to discover its state at the moment of fecundation, as well as imme- diately before and after that event.

The almost universal supposition, that the Purkinjian or germinal vesicle is the essential portion of the ovum, has been realized in these investigations ; but in a manner not anticipated by any of the numerous conjectures which have been published. The germinal vesicle becomes filled with cells, and these again become filled with the foundations of other cells ; so that the vesicle is thus rendered almost opake. The mode in which this change takes place is the