AND ON THE DIRECT AGENCY OF THE SPERMATOZOON. 
279 
during one hour, and when there was reason to believe that the majority of them had 
perished, but when there were still a very few among them in motion, having either 
revived, or but recently escaped from spermatozoal cells contained in the fluid. No 
impregnation took place in either of these instances. 
Thus the results of these experiments appear to show that the spermatozoon does 
not impregnate when entirely deprived of its power of motion hy narcotization, and 
disenabled to penetrate into the envelopes of the egg; and, consequently, that its 
fecundatory power has a close relation with its motion, or force of vitality. In this, 
then, they coincide with those of the previously detailed experiments, and go with 
them to show that the act of fecundation of the egg of the Frog, and probably also of 
all the Vertebrata, is the result of a power in the spermatozoon, which, in its operative 
condition, is characterized hy motion ; and that this power is totally independent of 
everything approaching to volitional influence, in the impregnating body, but seems 
to be in direct relation to physical causes. 
MM. Prevost and Dumas appear to have thought that the spermatozoa which they 
observed within the egg-envelopes had entered through means of the infiltration, or 
imbibition of water by the envelopes ; and the gist of their experiments was to show 
that particles of solid matter do enter during such infiltration, or, as it has since been 
designated, endosmosis. But some experiments, elsewhere detailed*, have led me to 
believe, that only such solid particles as are very much smaller in diameter than the 
spermatozoon can so enter with the water by endosmosis ; while the circumstances 
now detailed fully prove that the entrance of the spermatozoon is not the result of 
simple infiltration, but is that of the operation of direct mechanical or physical power 
in that body. Thus, if it were mainly dependent on endosmosis, the perfectly motion- 
less spermatozoon would enter the tissues and fecundate the egg equally well with 
the active, but this, as we have seen, is not the case, and this was shown by the 
physiologists now referred to. On the other hand, the circumstance that the spermato- 
zoon invariably enters the tissues with its thicker or body portion directed forwards, 
and sometimes even at an angle slightly inclined to the centre of the yelk, and always 
impelled by an oscillatory or vibratile motion of its caudal portion, seems to show 
that its power of penetration is not only a necessary condition of its function, but is 
inherent as such in its organic composition. It may yet be true, nevertheless, that 
the passing of the spermatozoon through the substance of the envelopes to the vitel- 
lary membrane may be indirectly aided by the endosmic action of the envelopes. 
But this aid does not consist of any imbibing property in the tissues. It appears to 
be simply of a negative character, and to be the result of a decrease of density in the 
tissues, which, through their imbibition of water, and consequent expansion, are 
caused to offer less and less resistance to the propulsive force of the spermatozoon. 
This I believe is the proper explanation of the fact of penetration by this body. 
But although penetration be not caused by the endosmic action of the envelopes, 
* Philosophical Transactions, 1851, p. 224. 
