THE OVUM IN THE AMPHIBIA. 209 



of drops as they passed the last filter, and of portions from the capsule it was caught 

 in, there was only one instance of the presence of spermatozoa. In this I saw two, but 

 perfectly motionless. The fluid that passed through the first or top filter, I had 

 reason to suspect was contaminated by a small quantity having travelled over the 

 sides of the filter. I knew also, that a few spermatozoa always penetrate through a 

 single filter, or rather perhaps are carried through by the fluid. Accordingly, I de- 

 tected several spermatozoa in this portion. The fluid that remained in the interior of 

 this filter abounded with very active ones. It was not employed until fifty-three 

 minutes after it had been procured from the Frog. 



No. 1. Seventy ova were passed on a dry surface, and a portion of the fluid which 

 had traversed three filters was poured carefully over them, and water was then added. 



In four hours and twenty-five minutes I found one ovum partially impregnated, and 

 the yelks of others were somewhat shrunk, and a little irregular, an appearance fre- 

 quently seen in ova that have not been impregnated. Not a single ovum, however, 

 was fruitful. 



No. 2. One hundred and twenty-seven ova were shed into water on the second of 

 the three filters, which still retained a portion of the fluid from the first, and in 

 which I had found a few spermatozoa. At four hours and fifty minutes several of the 

 ova had begun to be divided, and out of this set of eggs sixteen embryos were pro- 

 duced. 



No. 3. One hundred and sixty-three ova were passed into water on the topmost of 

 the three filters, and four hours and fifty minutes afterwards a very large proportion 

 of them had become segmented, as was expected, although from the circumstance of 

 the seminal fluid having been more than one hour mixed with water before it was 

 employed, the number was not so great as usual. But it was not entirely due to 

 this cause. Many of the ova had been injured before impregnation, and these became 

 irregular and pear-shaped. At the end of twelve days forty-nine well-developed em- 

 bryos had been formed. 



SetN. April 4, 1850. 



Four filters were now used instead of three, the seminal fluid being obtained and 

 mixed as before. The fluid which had passed through the whole of these filters, con- 

 tained not a trace of spermatozoa or of the nuclei of cells. That which had passed 

 through two only still gave an occasional perfectly motionless spermatozoon, but 

 not a single one in motion ; the fluid from the uppermost or first filter, as in Set M, 

 still swarmed with myriads of active spermatozoa. It was thus proved that the filtra- 

 tion was complete. 



No. 1 . One hundred and thirty-one ova were passed on a dry surface, and a portion 

 of the fluid which had traversed the four filters was poured over them, and water was 

 then added. But not a single ovum gave any sign of having been impregnated, not 

 one became segmented, nor was a single embryo produced. The ova became slightly 

 irregular, shrunken, and depressed at parts of the yelk, a condition which, as I had 



MDCCCLI. 2 E 



