THE OVUM IN THE AMPHIBIA. 
205 
No. 6. Thirty drops of Jiltet'ed fluid were added to one ounce of water with two 
hundred and ten ova. At the expiration of five hours two ova had become segmented, 
and two embryos were afterwards produced. 
No. 7. Thirty drops of diluted fluid, not flltered, were added to water with two hun- 
dred andflfty ova. At four hours and forty-two minutes segmentation had commenced 
in two or three of these, and in jive hours had occurred in almost every ovum. Nearly 
the whole of these produced embryos. 
No. 8. About thirty drops of the same diluted fluid, not filtered, were added to 
water that contained about two hundred ova, passed from the body of a frog killed 
twenty hours before. A few of these ova became imperfectly segmented, but not 
one produced an embryo. 
From these first experiments with filtered fluid, it seemed that the portion of semen 
which passes through the filter has not the power of impregnating, unless there are 
spermatozoa present in it ; while similar quantities of diluted semen that has not been 
filtered, are efficient and impregnate, as in Nos. 4, 5, 6 and 7* Further, it is shown, 
from No. 8, if we may judge from one experiment, that ova which have remained in 
the body of a frog twenty hours after actual death and cessation of the organic func- 
tions, and in a temperature of 55° Fahr., may be affected by the stimulus of the im- 
pregnating fluid, but not sufficiently so perhaps as to result in fruitful impregnation. 
During the time these ova were under observation, in March 1849, an opportunity 
occurred of observing the effect of reduced temperature on the rate of development 
of the embryo when its formation has been somewhat advanced. On the seventh, 
eighth and ninth days after impregnation of the ovum, and when the temperature 
had already been considerably reduced, the season became severe, and in order to 
test the effects of cold, the eggs were removed to the open air and exposed to a keen 
wind. The temperature of the atmosphere was then 38° Fahr. During the night of 
the tenth day, the water in which the ova were contained was frozen to a mass of ice. 
Yet many of these ova, as above shown, produced embryos. Spallanzani had already 
remarked, that the eggs of the Frog may be inclosed in ice, and yet afterwards pro- 
duce embryos, if the envelope does not become frozen*. 
The experiments made to ascertain whether cleavage of the yelk may be taken as 
a test of impregnation (p. 190), seemed also to show that, within certain limits, a 
large or small quantity of seminal fluid has some influence on the more or less early 
occurrence of this phenomenon. It occurred to me, therefore, that in making the 
experiments now given, two questions might be examined : one, as to whether the ex- 
tremely minute quantities of seminal fluid disseminated in water, as mentioned by 
Spallanzani, are as efficient to produce the embryo at the low temperature of the 
season at which the Frog spawns in this country, as in the warmer region of 
Italy; and the other, whether the presumed efficiency of such minute quantities de- 
pended on the presence of the spermatozoa; and it seemed possible to put these 
* Dissertations, &c., vol. ii. p. 49. 
