THE OVUM IN THE AMPHIBIA. 
207 
But however satisfactory these experiments were with regard to that fact, they still 
left the question of the immediate agency of the spermatozoa in impregnation in 
doubt. I therefore repeated them with greater precision, and with that object only 
in view, and took especial care to obtain as perfect a filtration and separation of the 
spermatozoa from the fluid as possible. The results were far more interesting and 
instructive than I had anticipated, as I found by repeated examination by the micro- 
scope that the filtered fluid was almost completely deprived of spermatozoa, one or 
two only being occasionally detected in it, with a very few nuclei and spermatozoa! 
cells. One circumstance that tended to increase the value of this set of experiments, 
and to prove the influence of the spermatozoa, was, that the ova employed were not 
fully matured, and hence I had less expectation of a favourable result. The quantity 
of seminal fluid obtained was larger than usual, and this was mixed with twice its 
quantity of water. This mixed fluid was divided, as before, into two portions, one of 
which was filtered, and the other not. The experiments were commenced in the 
early part of the day, and the temperature of the atmosphere of the room, and that of 
the water employed, was nearly the same, 51° Fahr., and the whole of the experi- 
ments were placed as nearly as possible under similar circumstances. 
Set L. March 18, 1849. Atmosphere 51° Fahr. Water 51° Fahr. 
No. 1. Ten minims of the mixed fluid were added to two ounces of water, into 
which one hundred and fifty ova were immediately passed. One hour afterwards I 
found a great abundance of spermatozoa adhering to the surface of the envelopes. 
Segmentation of the yelk commenced in five hours and forty minutes in a few ova ; 
and took place in others at a later period. A few only of these ova produced em- 
bryos. 
No. 2. Ten minims of the filtered portion of the mixed fluid were added to two 
ounces of water, and about one hundred and fifty ova were passed into it. When 
these ova were examined at the expiration of an hour, not a single spermatozoon was 
detected on any of them ; and when repeatedly examined at the end of five and six 
hours, not one showed any signs of cleavage. This change did not take place in any 
of them even at a later period, and not one produced an embryo. 
As the ova in these two experiments were the first that passed from the body of the 
Frog, it was fair to regard them as being the most matured ; segmentation ought, 
therefore, if it occurred at all, to have taken place at an earlier period in these than 
in others afterwards obtained from the same female. 
No. 3. The filter paper employed in separating the fluid used in the last experi- 
ment, No. 2, and which retained the separated spermatozoa in a minute quantity of 
fluid that had not passed through, was placed in two ounces of water, and one hun- 
dred and thirty ova from the same female were shed upon it. When some of these ova 
were examined at the end of an hour and a half, spermatozoa in vast abundance 
were found adhering to every part of their surface, but the whole were then motion- 
less, and apparently dead and partially coiled on themselves (Plate XIV. fig. 8 c). In 
