AND ON THE DIRECT AGENCY OF THE SPERMATOZOON. 269 



ances of spermatozoa in the interior of the jelly, although they were in abundance 

 at the point on the surface, to which they had been applied by the pin. Neither 

 of these eggs underwent any change. But in a fourth trial, with an egg immersed 

 for ten minutes, and to which the spermatozoa were applied in the same way as in the 

 preceding, I saw, at the expiration of fifty minutes, four spermatozoa sticking in the 

 vitellary membrane ; soon after which the chamber was commenced, and at a later 

 period segmentation of the yelk took place, and an embryo was produced. This was 

 with fluid which had been obtained nearly an hour before it was employed. In a 

 further trial, with an isolated egg, to which a full quantity of fluid was added, by 

 three or four applications of the loaded pin's-head, after the egg had been one minute 

 in the water, I detected several spermatozoa, within half an hour afterwards, sticking 

 like the preceding into the vitelline membrane, and this egg also produced a good 

 embryo. 



It was thus evident, that in some cases, spermatozoa certainly penetrated through 

 the envelope ; but as there was also one instance, in which the egg had become 

 fecundated, and afterwards produced an embryo, in which I had not seen sperma- 

 tozoa within the envelopes, it was necessary to pursue the investigation further, to be 

 quite assured of the fact of penetration as connected with the act of fecundation. 



On the following day an opportunity occurred to me of examining the egg after 

 impregnation by the natural union of the sexes. I had several pairs of frogs in 

 a basin of water covered by a glass bell jar. when, having my attention directed for 

 a few minutes to some other object, one pair of frogs spawned suddenly, as I knew 

 by the sound of a plunge or splash in the water, which always occurs after the act, 

 at the moment of separation of the sexes. Nearly the whole of the eggs were depo- 

 sited in a mass, but there were a few which were detached from the rest, and were 

 lying at the bottom of the water. This seemed a good opportunity to examine these 

 eggs, which had been expelled naturally, singly, in search of the spermatozoa within 

 the envelopes. Fifteen of these detached eggs were placed, each in separate cells, 

 and carefully examined, during the first hour and a half after their expulsion. In 

 the first eight or nine of these eggs, I was not able to detect even a single spermato- 

 zoon within their substance, and I began to look upon the previous observations, 

 made by artificial impregnation, rather as the result of accident. In the tenth egg, 

 however, I most distinctly saw spermatozoa in contact with the vitellary membrane, 

 but in one or two eggs examined after this no spermatozoa were to be seen. Out of 

 the fifteen eggs examined, there were only two in which I could detect spermatozoa. 

 As each egg had been carefully marked, and a note made, as to whether or not 

 any spermatic bodies had been detected within it ; and as previous investigation had 

 shown, that when any fecundation has been effected the yelk of the fecundated egg 

 becomes depressed, and a chamber begins to be formed, in about one hour, or little 

 more, after the spermatozoon is supplied to the egg, between its upper surface and 

 the investing membrane, there were ready means of learning, within a short time, 



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