THE OVUM IN THE AMPHIBIA. 
191 
3. SUSCEPTIBILITY OF THE OVUM. 
I was not aware, at the time of commencing my experiments in March 1849, nor 
indeed until very recently, of the extent to which the original investigations of Spal- 
lanzani, and of Prevost and Dumas had long ago been carried*, and it has only been 
since my experiments were completed, and during the preparation of this paper for 
presentation to the Royal Society, I have learned by careful reference to their first 
memoirs, that they have anticipated me in part of this inquiry — that of endeavouring 
to separate the spermatozoa by filtration from the more fluid portion of semen, and 
testing the effect of these two constituents in artificial impregnation. To them 
therefore be all honour for the result ; although even they, as they honourably men- 
tion, had themselves been anticipated in this by Spallanzani, and that too with 
similar success. The extraordinary results obtained by Spallanzani'!' in artificial im- 
pregnation, and the imperfect knowledge which we possess of the nature of the means 
by which it is effected, has induced me to endeavour to repeat and vary his experiment, 
and to conceive others, which, so far as I am aware, have not yet been attempted. I 
have been the more urged to this from the circumstance mentioned by Spallanzani, 
and already alluded to (p. 189), the occasional supposed absence of spermatozoa from 
fluid that is capable of fecundating; and also from a belief formed long ago with 
regard to the Articulata, that the spermatozoa, nevertheless, certainly are the efficient 
agents in impregnation, although full proof of the fact has been wanted. I have 
been desirous therefore of learning how far this belief can bear the test of direct 
experiment, or the fact be capable of demonstration by artificial means in the Am- 
phibia. As, however, the experiments I have myself made vary from those of the 
authors mentioned, — have not been influenced by the result they had previously 
arrived at, — have been somewhat more extended, and, as I believe, will now tend to 
place the fact of the direct agency of the spermatozoa in impregnating the ovum 
beyond doubt, — it has seemed desirable still to give them in detail, as assisting to 
establish an important point of knowledge by facilitating a comparison of the results 
of independent investigations. 
Duration of susceptibility . — The length of time during which the ovum, after it has 
been passed, remains susceptible of fecundation, is affected by several circumstances. 
I had reason to believe at the commencement of my experiment that this time is very 
short. Spallanzani found that when the egg of the Toad was expelled into water it 
was not susceptible of fecundation after a lapse of fifteen minutes:};. This was at a 
raised temperature of the atmosphere, 81°‘5 Fahr. On the other hand, he also found 
that, at this temperature, ova retained fourteen hours within the body of the female 
after death, and of course not in contact with air or water, might still be fecundated; 
and that when preserved in an ice-house fecundation might be effected at two days 
after the death of the parent^. But Prevost and Dumas arrived at the conclusion || 
* Annales des Sciences Naturelles, tom. i. et ii. 1824. t Dissertations, &c. vol. ii. 
+ Loc. cit. vol. ii. p. 178. § Loc. cit. vol. ii. pp. 176 and 177. || An. des Sc. Nat. vol. ii. p. 135. 
