AND ON THE DIRECT AGENCY OF THE SPERMATOZOON. 271 



At the expiration of three hours from the commencement of these observations, 

 although the number of spermatozoa which had first been noticed within the coverings 

 of the eggs submitted to examination appeared to have been diminished, there was still 

 an abundance attached to the vitellary membrane. These appeared to afford a good 

 opportunity for endeavouring to ascertain whether any part of the body of the sper- 

 matozoon is passed through the membrane into the cavity of the yelk. With this 

 object in view, I placed a glass cell, which contained an egg, on one side, and waited 

 for the rotation, or rather the gravitation, of the yelk within its envelopes. By this 

 change of position of the yelk within its coverings and which always takes place, if 

 fecundation, or any change in the position of the entire egg, has been effected, the 

 flattened surface of the yelk, and the chamber above it, were brought beneath that 

 part of the vitellary membrane into which spermatozoa appeared to have sunk 

 deepest, so that if any of these bodies had passed, or were in the act of passing, or 

 had been partially protruded through the membrane into its cavity, which contained 

 the yelk, it was fair to expect that they might thus have been detected. But not the 

 slightest trace of penetration, even by a single spermatozoon, could then be observed*. 



I may here remark, in anticipation of a future communication, that, previous to 

 segmentation, the mass of the yelk does not appear to be invested by any distinct 

 envelope within its so-called vitellary membrane, but the whole seems to be kept 

 together by the natural coherence of the granules or cells of which it is composed ; so 

 that when the position of the egg is changed the yelk mass rotates within the vitel- 

 lary envelope as a consequence of this change, owing probably to the excentric posi- 

 tion, within its substance, of the progeny of the germinal vesicle-f-, contained in the 



* Since this paper was communicated to the Society, I have succeeded, through the adoption of a different 

 mode of examination, in detecting spermatozoa within the vitelline cavity in direct communication with, and 

 penetrating into the yelk. They were first seen by myself, in company with a friend, on the 25th of March of 

 the present year (1853) within the clear chamber above the yelk, at about forty minutes after fecundation, 

 when the chamber begins to be formed. I have since repeatedly observed them within the chamber, and in 

 some instances still in motion, in which state I have had opportunities of showing them to my friend Professor 

 ELLIS of University College, and to two other medical friends, so that the presence of active spermatozoa within 

 the vitelline cavity in the fecundated egg of the Frog may now be regarded as indisputable. The details of my 

 investigation I reserve for a future communication, and will merely now add, that the spermatozoa do not reach 

 the yelk of the Frog's egg by any special orifice or canal in the envelopes, but actually pierce the substance of 

 the envelopes at any part with which they may happen to come into contact ; as I have constantly observed while 

 watching their entrance : sometime after they have entered the yelk chamber they become disintegrated, and 

 are resolved into elementary granules. The importance of this fact of actual penetration by the spermatozoon 

 into the yelk is indicated by WACNEK and LEUCKARDT, in their late Article, " Semen" (loc. cit. p. 507), in the 

 following remark: "The truth is, the 'how' of the fecundation is as far from our knowledge to-day as it 

 was thousands of years ago ; this process is still enveloped in what we feel inclined to consider ' its sacred 

 mystery.' It would be different if we could prove that the spermatozoa really yielded the material foundation for 

 the body of the embryo ; that they penetrated into the ovum, and were developed into the animal (which was the 

 assumption of LEEUWENHCEK, ANURY, GUATIER), or else, that they became metamorphosed into the central parts 

 of the nervous system." G. N., April 18, 1853. 



f Philosophical Transactions, Part I. 1851, p. 176. 



