266 MR. NEWPORT ON THE IMPREGNATION OF THE OVUM TN THE AMPHIBIA 
numbers. Thus the spermatozoa, like the ova, are more efficient at a given tempera- 
ture, within the first two or three m.inutes after they are passed from the body, than 
at abater period. At that time there is not only a greater number of spermatozoa in 
a given quantity of fluid in a state of activity ; but the whole of them exhibit a 
greater intensity of motion than after they have been for some time mixed with water. 
In the Toad, which, in this country, as already stated, pairs at a few weeks later m 
the season than the Frog, and which seems not only to require a higher temperature 
of the surrounding medium, but also a relatively higher temperature for the develop- 
ment of the ova, the spermatozoa are most active, and most fitted to impiegnate at 
the instant of expulsion ; as is shown in the mode of intercourse of the sexes in that 
animal, and in the fact that, if the fecundatory fluid be not immediately applied to 
the strings of ova as these are passed, the unsprinkled ova are infertile. The oviposi- 
tion of the Toad is an exceedingly slow process, and usually lasts, as Spallanzani 
observed, from ten to fifteen hours; in one instance I found it continued during 
seventeen hours, but it was completed in others in eight or ten. The act of impreg- 
nation, therefore, is necessarily also prolonged. But the length of time during which 
the spermatozoa continue efficient to impregnate after removal from the bod}, is 
shorter than in the Frog. Spallanzani found that, at a temperatuie of 81 Fahr., 
it does not exceed fifteen minutes. I also have noticed that the motions of the 
spermatozoa cease much earlier than in the spermatozoa of the Frog. 
Thus the conclusions to be drawn from the facts of natural impregnation in the 
Toad, fully agree with those deduced from artificial impregnation in the Frog, and 
seem to establish the view, that while an increase of temperature is required for the 
fulfilment of the reproductive function in that animal, and to maintain the efficienc} 
of the spermatozoa, the fecundatory force of the agent is of shorter duration, and 
corresponds to its more early cessation of motion. 
13. PENETRATION BY THE SPERMATOZOON IN EFFECTING FECUNDATION. 
The penetration of the spermatozoon into the substance of the egg, or even into 
its envelopes, has been so much disputed, and so repeatedly denied, that it is only ou 
what may perhaps be regarded as indisputable evidence, that any one ought to re- 
assert it. Up to a very recent period I could not, myself, admit it as probable ; 
because, throughout my investigations, I had not been able to detect any appearance 
in the fecundated egg or its envelopes, either of the Frog or Newt, which rendered it 
likely that the spermatozoon penetrates into or through them. Yet the fact of pene- 
tration was stated by the older naturalists, not so much, perhaps, from any decided 
proof of its occurrence, as from a confidence that it was only in this way that the 
function of the spermatozoon could then be understood. Leeuwenhoek, and those of 
his day, not only believed that the spermatozoon penetrates bodily into the substance 
of the egg, but also that it becomes the future embryo. In later times, M. Prevost 
having, with M. Dumas, seen the spermatozoon within the gelatinous envelope of the 
