THE OVUM IN THE AMPHIBIA. 
221 
Twenty-six of these ova became impregnated and produced embryos ; thus showing 
that impregnation takes place very quickly, and is not prevented by the addition of 
a dense colouring fluid, added after contact with the impregnating fluid. 
No. 3. Forty-one ova were passed into a solution of carmine in water which had 
been mixed with seminal fluid immediately before the passing of the ova. 
Thirty-three of these ova also produced embryos. It was evident, therefore, that 
when seminal fluid is freely mixed with a dense medium that holds solid particles of 
matter in suspension, the spermatozoa are not necessarily prevented from effecting 
impregnation of the ova. Thus the ova of the Frog, although usually deposited in 
slow-running or clear still water, may be deposited even in slightly turbid water 
without impediment to the natural process of impregnation, as the water and sper- 
matozoa may be brought into contact with the ova at the same instant. 
No. 4. Thirty ova were passed into water mixed with fluid that had been almost 
completely deprived of spermatozoa by filtration. 
Only one ovum exhibited any signs of impregnation, but not a single embryo was 
produced. 
No. 5. About two hundred and twelve ova were passed into a dense solution of car- 
mine and water in which the filter paper with spermatozoa, separated from the fluid 
employed in No. 4, had already been placed, and the water and ova were then freely 
agitated together. 
The result of this experiment was very marked. Only a few of these ova became 
segmented, and the change proceeded much slower in them than in the ova of expe- 
riments Nos. 2 and 3. At the end of twelve days on\y Jive embryos had been pro- 
duced. Thus a dense solution of carmine, applied to the spermatozoa before they are 
brought into contact with ova, may have the effect of preventing impregnation, appa- 
rently by operating as a mechanical impediment. These ova, excepting only a few 
removed for the following experiment, No. 6, which were taken from the mass as 
stated, were allowed to remain in the carmine for twenty-four hours before they were 
placed in clear water. 
No. 6. Forty ova taken from the last experiment were removed to clear water at 
the end of one hour and a quarter, having first been thoroughly washed. The result 
was as decided as in No. 5. Only two embryos were formed; so that there was 
further reason to believe that impregnation takes place very quickly, and that the 
result in No. 5 was not entirely due to long continuance in the solution, but to some 
impediment at the time of contact. 
No. 7. A thick solution of carmine was mixed with seminal fluid and water, and 
three minutes afterwards a mass of ova were passed into it. 
This experiment was similar to No. 3, excepting only that the solution of carmine 
was much more dense, and the ova were not passed until three minutes after the 
fluids had been mixed. There was a marked difference in the result. Only a few of 
these eggs became segmented, and only eight out of a large mass produced embryos. 
