THE OVUM IN THE AMPHIBIA. 
241 
much the most frequent occurrence when the ova are placed in dense fluid before 
contact with the spermatozoa, as in the experiments with carmine. Lastly, when the 
ova are only partially impregnated they are usually, and perhaps always unpro- 
ductive. 
These facts lead us to inquire, whether impregnation takes place through any cata- 
lytic influence of the spermatozoa as suggested by Bischoff*, while in a state of 
activity, and at the instant they are brought into contact with the ovum, or whether 
impregnation results from a diffluence of the spermatozoa thus brought into contact 
with the surface, the substance into which they may be dissolved being carried by 
endosmosis with the water imbibed through the tissues ; or whether it is the result 
of the conjoint influence of both these conditions ; — the first action induced being 
instantaneous and catalytic, and possibly dependent on the persistence of organic 
vitality in the spermatozoa, while the completion of the impregnation may depend on 
the imbibition of some material influence or substance derived from the impregnating 
body ; — a view which the gradual disappearance of the bodies of the spermatozoa 
from the surface of the ovum, both in the Frog and Newt, seems to favour; as we 
have already seen that endosmosis is an active and important function of the enve- 
lopes of the ovum at the very period when impregnation is effected. 
All the experiments now detailed seem to show that in those vertebrata which 
expel their ova into water before impregnation, as in the tail-less Amphibia, and in 
which — from the nature of the medium into which the ova are passed — we may 
infer that the function takes place most quickly, impregnation is commenced at 
the very instant of contact of the spermatozoon with the ovum, and even may be 
completed within very short spaces of time — but duration of at least some seconds 
of actual contact, — even in these animals’ ova, is essential to the perfection of the 
function ; — but this period, we may fairly conclude, may differ in different classes of 
animals, and possibly may have some relation to the greater or less facility with which 
the spermatozoa are brought into contact with the ova. 
When the experiments last detailed are compared, — the effects produced by the ap- 
plication of media which influence the spermatozoon and the ovum chemically, — with 
those of which the effect is merely mechanical, we seem to have made some advance 
towards a future knowledge of the nature of the impregnating power. Although we 
are as yet entirely without proof that any material influence or substance is actually 
transmitted from tbe spermatozoon on the surface of the ovum to the yelk in the in- 
terior, we have evidence that fluids are imbibed by the ovum by endosmosis through 
its tissues ; and although not a trace of the spermatozoon is detected in the interior 
of the ovum, we have seen that it remains for a long time on the surface, and gradu- 
ally disappears, apparently by diffluence ; so that it may be fair to conclude, that the 
agency of this body is material in its operation. On the other hand, the effect which 
we find*is produced on the yelk by the direct and even momentary contact of the 
* Muller’s Archives, 1847. 
2 H* 
MDCCCLI. 
