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 letaining, 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 difiiuence 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 
leas 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 
