104 



mity of an axis, and the author proceeds to show how the latter 

 attraction can be found and reduced to elliptic functions. He then 

 gives this proposition : 



Let , b, c be the semiaxes of a homogeneous fluid ellipsoid, and 

 A, B, C the forces acting on points at the extremities of a, b, c, 

 caused partly by the ellipsoid's own attractions on its parts, and 

 partly by centrifugal forces of revolution about an axis (2c), or by 

 the action of an extraneous force directed towards its centre, and 

 varying as the distance from the centre, then the ellipsoid will pre- 

 serve its form if Aa=B6=Cc. 



The last proposition stated in the paper is thus given : let R and r 

 be the radii of two homogeneous concentric spheres ; A and the 

 attractions of each on a point on the surface of the other, then 



A a 



= , whatever be the law of attraction as a function of the di- 



R2 r * 



stance. 



The demonstration given of the first of these two theorems is very 

 concise, and of the second is direct and elementary. 



VI. " Researches on the Impregnation of the Ovum in the Am- 

 phibia ; and on the Early Stages of Development of the 

 Embryo." (Third Series.) From the MS. papers of the 

 late GEORGE NEWPORT, F.R.S., F.L.S. &c. Selected and 

 arranged by GEORGE VINER ELLIS, Esq., Professor of 

 Anatomy in University College, London. Communicated 

 by Sir JOHN FORBES, M.D., F.R.S. Received June 6th, 

 1854. 



In this paper the author has given the result of further inquiries 

 into the manner by which the frog's egg is impregnated, and has 

 supplied in addition some very interesting facts respecting the de- 

 velopment of the embryo during the earlier stages of its growth. 



In consequence of the difficulties that arose in the course of the 

 inquiry, and of the doubts that might be suggested by others from 

 the difficulty of manipulating with the egg of the Amphibia unless 

 certain precautions are taken, the author first describes the apparatus 



