AND ON THE DIRECT AGENCY OF THE SPERMATOZOON. 275 



through the vitelline membrane which it covers. This mode of disappearance 

 certainly is that by which the spermatozoa might be supposed to penetrate to the 

 yelk, if in reality they do so*. Thus, presuming the body, or thicker portion of the 

 spermatozoon, to perforate and pass through the vitelline membrane, the more 

 slender or tail portion would follow quickly. But if this occurs with some, then it 

 would be fair to expect that it would happen to the whole which arrive at and become 

 partially imbedded in the membrane ; especially to those which have sunk into it to 

 a depth equal to one-half the length of the thicker or body portion ; or, further, that 

 the progress of others might be arrested before they had completely passed into the 

 vitelline cavity ; and, consequently, that some would occasionally be seen protruding 

 into the interior. But I was not able, in the instance of the observations now detailed, 

 nor in others afterwards made, to prove either of these suggested conditions. 



In the observation now referred to, as well as in others since made, there were 

 many spermatozoa which remained distinctly visible for several hours, in the same 

 place, and in almost precisely the same position, sticking into the vitelline membrane, 

 and retaining, at the end of a lengthened period, the same appearance as at first, 

 excepting only that they seemed to have become smaller in diameter and to have 

 their caudal portion more looped. In the present instance, at the high temperature 

 of 65 FAHR. to 66 FAHR., not only were they distinctly seen at the commence- 

 ment of segmentation of the yelk, which happened at the end of three hours and 

 twenty-two minutes, but many of them were present until after the yelk had under- 

 gone several of its subsequent divisions. This was the case not only with those 

 which had arrived at the vitelline membrane, but also with others which had never 

 reached it, and had not penetrated further than to about the middle, or granulous 

 portion of the envelopes ; as happened with many spermatozoa, both in the eggs 

 which were fecundated naturally, as well as in those which were the subjects of ex- 

 periment, and were artificially affected. It was those which remained in the sub- 

 stance of the envelopes which usually disappeared earliest, becoming at first gradually 

 fainter, and then more undefined in outline. This change was supposed to be due to 

 a gradual diffluence of the substance of the spermatozoon, through the influence of 

 the water imbibed by the envelopes ; but whether this happened as part of the fecun- 

 datory process, or whether it was simply the natural process of decay, as other cir- 

 cumstances to be mentioned seemed to intimate, there was no distinct proof. It 

 was remarkable, however, with reference to the act of fecundation, that in almost 

 every instance, even of those spermatozoa which never arrived at the vitelline mem- 

 brane, the body portion was always directed towards the yelk, usually peripherally, 

 but sometimes inclined at slight angles to one side or the other; thus showing that 

 it is invariably the body portion which penetrates. 



* That this is really the fact, and that the actual penetration by the spermatozoon into the yelk chamber 

 was observed on this occasion, is now rendered almost certain by my recent observations stated in the preceding 

 note, p. 271. G. N., April 18, 1853. 



MDCCCLIII. 2 O 



