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 only 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^rernoved 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. 



