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, torn. i. et ii. 1824. t Dissertations, &c. vol. ii. 



} Loc. cit. vol. ii. p. 178. Loc. cit. vol. ii. pp. 176 and 177. II An. des Sc. Nat. vol. ii. p. 135. 



