192 
MR. NEWPORT ON THE IxMPREGNATION OF 
that the time is much more extended in the Frog ; — that fecundation may take place 
when the temperature ranges from 53° Fahr. to 59° Fahr. at the expiration of one 
hour after immersion of the eggs ; — that some eggs are fecundated at two, and a 
very few even at the end of three hours, after which no fecundation takes place. 
The results obtained by myself both on the Frog and Toad have been most in ac- 
cordance with those by Spallanzani. This is the more worthy of notice from the 
circumstance that a slight difference between his and mine is readily accounted for 
by a corresponding slight difference of temperature, which Spallanzani, and Pre- 
vosT and Dumas, have remarked, and since them also Mr. Bell*, has great in- 
fluence on the changes of the eggs and young. The temperature at which my test 
experiments were made, was a little lower even than that at which Prevost and 
Dumas made theirs ; and yet I was not able to find any ova susceptible of fecunda- 
tion after they had remained from thirty to forty minutes in water. On careful 
examination of Prevost and Dumas’ experiments, I think the difference may perhaps 
be due to a circumstance which seems equally to affect some of Spallanzani’s 
results, namely, the mode in which the impregnating fluid employed was obtained. 
These authors state that the fluid they employed was expressed from the testicles of 
the frogs, so that from what we now know of the mode of origin of the sperma- 
tozoa, this fluid in all probability contained a large proportion of developmental cells 
that included spermatozoa not fully matured, but which might become liberated in 
the water at a longer or shorter period. Or, possibly, the fluid added to ova that 
had been long in the water, had been very recently obtained ; in which case the 
vigorous spermatozoa might effect the impregnation of ova that had become almost 
insusceptible through the imbibition of water by their envelopes. I am led to this 
view by the fact that the jelly-like envelope of the Frog’s egg begins to imbibe and 
expand the instant it is brought into contact with fluid ; and from having ascertained 
that there is a close relation between the degree of expansion and imbibition of this 
envelope and the susceptibility of the ovum to become impregnated, and that these 
conditions are also greatly affected by temperature. The act of expansion of the 
envelope is an act of endosmose, and possibly this is one of the means by which the 
impregnating agent is made to exert its influence on the yelk. The yelk is not a 
passive recipient during the endosmic action of its coverings, but seems to partici- 
pate in that action, as I have seen portions of its surface heave and contract within 
the vitelline membrane during the first hour the egg has remained in water. It may 
thence be inferred, that if the impregnating stimulus be not supplied quickly, the 
fitness of the ovum to become impregnated is diminished in proportion as its enve- 
lopes are expanded. If then it be proved that the spermatozoon is the agent in impreg- 
nation, but, so far as can be discovered, does not penetrate bodily into the ovum or 
its envelopes, and yet, as may be shown, must always come into contact with their 
surface, the more rapidly and to the greater extent this expansion takes place, and 
removes the efficient body from that which it is in some way destined to affect, the 
* British Reptiles, p. 92. 
