496 Royal Society . 



The most important of the foregoing facts respecting the deve- 

 lopement of the mammiferous ovum, however opposed they may be 

 to received opinions, are in accordance with, and may even explain, 

 many observations which have been made on the developement of 

 other animals as recorded in the delineations of preceding observers. 

 If in the ovum of the bird the germinal vesicle in like manner re- 

 turns to the centre of the yelk, the canal and cavity known to exist 

 in the yelk of that ovum might be thus explained. The ovum may 

 pass through at least one-and-twenty stages of developement, and 

 contain, besides the embryo, four membranes, one of which has two 

 lamina;, before it has itself attained the diameter of half a line, a fifth 

 membrane having disappeared by liquefaction within the ovum. 



The size of the minute ovum in the Fallopian tube and uterus 

 affords no criterion of the degree of its developement ; nor do any 

 two parts of the minute ovum, in their developement, necessarily 

 keep pace with one another. 



The proportion of ova met with in these researches, which seemed 

 to be abortive, has amounted to nearly one in eight. Sometimes 

 two yelk-balls exist in the same ovum. With slight pressure, the 

 ovum', originally globular, becomes elliptical. Its tendency to as- 

 sume the latter form exists especially in the chorion, and seems to 

 be in proportion to its size. 



The author has discovered that when the germinal vesicle is first 

 seen it is closely invested by an extremely delicate membrane. This 

 membrane subsequently expanding is that in which the yelk is 

 formed. He has traced the chorion from stage to stage up to the 

 period when it becomes villous, and shows that it is not, as he for- 

 merly supposed, the thick transparent membrane itself of the ovarian 

 ovum, but a thin envelope closely investing that membrane, and not 

 appreciable as a distinct structure until the ovum has been crushed. 

 When the chorion first admits of demonstration as a distinct struc- 

 ture the ovum consists of three membranes, a state which the author 

 has seen in an ovum no farther advanced than about an inch into the 

 Fallopian tube. The chorion subsequently thickens and imbibes a 

 quantity of fluid presenting a gelatinous appearance. 



April 25. — A paper was in part read, entitled, " Account of Experi- 

 ments on Iron-built Ships, instituted for the purpose of discovering 

 a Correction for the Deviation of the Compass produced by the Iron 

 of Ships." By George Biddell Airy, Esq., M.A., F.R.S., A.R. 



Mfiy 2. — A paper was in part read, entitled, " On the Motion of 

 the Blood." By James Carson, M.D., F.R.S. 



May 9. — The reading of a paper, entitled, " On the Motion of the 

 Blood. "'By James Carson, M.D., F.R.S., was resumed and concluded. 



After'referring to his paper contained in the Philosophical Trans- 

 action's for 1820, relative to the influence of the elasticity of the 

 lun"-s as a power contributing to the effectual expansion of the heart, 

 and promoting the motion of the blood in the veins, the author states 

 that his object in this paper is to explain more fully the mode in 

 which these effects are produced, and to corroborate by additional 

 facts and observations the arguments adduced in its support, He 



