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 of^fty-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 oifortyjive 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 tivo hundred 
and twelve, there were fifty-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 suflScient 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 
