222 



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. 



May 7, 1840. 



JOHN WM. LUBBOCK, Esq., M.A., V.P. and Treasurer, in the 



Chair. 



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 



