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MR. NEWPORT ON THE IMPREGNATION OF 
of the semen appears to be constituted almost or entirely of spermatozoa, while 
scarcely any liquor seminis can be detected ; — and further, on the great improbability, 
perhaps impossibility, of the liquor seminis of those animals which expel their ova 
into water before impregnation being brought into contact with the ovum. But the 
same author justly remarks, that “even up to the present day this hypothesis of the 
influence of the liquor seminis has not met with any direct refutation.” To this 1 
may add, that however strong the presumption may be in favour of the agency of 
the spermatozoa in those instances in which a liquor seminis has not been observed, 
it affords no sufficient reason for disbelieving that the spermatozoa are not resolved 
into fluid at the moment of fecundation ; or that in those animals in which the liquor 
seminis occurs in abundance it is not that which impregnates the ovum. 
The question then, so far as proof is concerned, both of the direct agency of the 
spermatozoa, and of the non-efficiency of the liquor seminis in impregnation, remains 
open, as well also as that which involves the knowledge as to how impregnation is 
effected. 
It is to these questions that this communication which I have now the honour of 
laying before the Royal Society is chiefly directed. I propose first to show the time 
and mode of disappearance of the germinal vesicle, and the condition of the ovum in 
the Frog and Newt, immediately before and after impregnation, and to endeavour to 
supply proof from actual experiments that the spermatozoa alone, in all cases of com- 
munion of the sexes, are the sole agents in impregnating the ovum ; and further, that 
impregnation cannot be effected by the liquor seminis; and next to examine in what 
way the agency of the spermatozoa is influenced, impeded, or exerted. 
1. CHANGES IN THE OVUM WITHIN THE BODY. 
The ovum of the Amphibia has so frequently been the subject of examination by 
the best observers that a further detailed account of its development may at first ap- 
pear to be useless, after what we already know of its changes through the labours of 
Swammerdam, Leewenhoek, Roesel, Spallanzani, Prevost and Dumas, Rusconi, 
Baer, Reichert, Vogt, Bell and others. But apart from the fact already men- 
tioned, that the ovum of the Amphibia affords us the best means of actual experiment 
on impregnation, there are questions which relate to its earlier conditions on which 
the observers named are not agreed, but which are of importance with regard to the 
physiology of reproduction in the whole of the vertebrata. 
I shall state, therefore, what I have myself observed with regard to these questions 
from the time when the ovarian ovum is approaching to maturity to that of its expul- 
sion from the body, before entering on the subject of its impregnation. 
As our means of comparing and testing the accuracy of all observations in natural 
history, and of experimental results in physiology, depend mainly on the correct 
identification of the objects examined, I may here state at once that the objects of 
the following details have been the Frog, Rana temporaria, and the Toad, Bufo vul- 
