THE OVUM IN THE AMPHIBIA. 233 



second afterwards the impregnating fluid with spermatozoa, no impregnation, or but 

 a very partial one, was effected. The ova in these three experiments amounted to two 

 hundred and six, and yet only one ovum became very partially affected. A like result 

 ensued even when the weaker solution was employed at an interval of two seconds, as 

 in Q 5, when out ofjifty-four ova segmentation occurred but in one. 



When the interval between the application of the impregnating fluid, in the first 

 instance, and that of the solution subsequently, was extended to Jive seconds, then a 

 greater proportion of ova became segmented, as in Q 1, with the weak solution, when 

 out of forty-Jive ova twelve became changed. 



These were the results when the experiments were made at different temperatures, 

 as at 49 FAHR. with the Set Q, and 60 FAHR. with the Set R. They cannot, therefore, 

 be attributable to inertness of the fecundating agent, or of the object to be fecundated, 

 occasioned by an unfavourable temperature of the surrounding medium. The fact 

 of the occurrence of segmentation in some ova, but not in the majority of the ova of 

 different experiments, as in Q 1, 2, 3 and 4, seems further to show that the influence 

 of the momentary application of the potash solution was produced chiefly, and in the 

 first instance, on the spermatozoa, or impregnating bodies, and not so immediately 

 on the ova ; since if the ova had been first, or most affected, none of them, probably, 

 would have become impregnated. 



Further, I may perhaps be allowed to remark, that the arrest of impregnation was 

 due mainly to the nature of the chemical agent employed; and the extent of inter- 

 ference with the fecundatory process was in proportion to the more or less immediate 

 action of this agent on the spermatozoon. Thus we have seen that but few ova were 

 impregnated when the solutions of caustic potass were employed; but when the 

 nitrate of potass was used as in Q 7, forty-three out of seventy -seven ova were seg- 

 mented; while in R 6, 7 and 8, in which the total number of ova was two hundred 

 and twelve, there werejifty-three segmented, and these produced forty-seven embryos. 



The object of these sets of experiments, therefore, that of endeavouring to ascer- 

 tain within what period of time after the contact of the spermatozoon with the ovum 

 its fecundatory function is exerted, appears to have been somewhat fulfilled ; in so 

 far as that in these experiments on the Amphibia the commencement of the act of 

 impregnation appears to have been almost instantaneous. Yet there seems reason to be- 

 lieve that momentary contact of the impregnating body, even in the ovum of these 

 animals, is not in itself sufficient to complete the fecundation, although it may tend to 

 induce that condition of the yelk, segmentation, which we now are assured is always 

 indicatory of its having been influenced by the fecundatory agent. If momentary 

 contact were sufficient for the completion of the function, then partial impregnation, 

 which so frequently takes place when spermatozoa are few in number, or in contact 

 only for very brief periods, could hardly happen ; while every ovum in which the 

 process of cleavage is begun ought to pass through all its changes to the production 

 of the embryo, circumstances being favourable to its development. But this we have 



MDCCCLI. 2 H 



