THE GROWTH OF THE EMBRYO IN THE FROG. 
233 
increase from the lamp, and by using pure sperm that had been obtained an hour 
before. 
At 12 b 50 ra a single egg was immersed in undiluted male fluid. 
At twenty-two minutes after immersion I saw spermatozoa passing through the 
vitelline membrane at all points of its surface, whilst some had passed through it. 
The yelk was beginning to separate from its membrane, and its surface had an undu- 
latory motion. As the chamber enlarged, several spermatozoa became evident within 
it in motion. 
At l h 45 m several of the spermatozoa were fast disappearing, as if breaking up into 
granules, but those outside the membrane did not disappear so rapidly as those 
within the chamber. 
Some other eggs, four in number, were experimented on with some of the same 
fluid used for the egg referred to above, and in this case the fluid had been removed 
from the male for two hours and a quarter; the fluid remained on the eggs half an 
hour, and its place was then supplied by pure water. Temperature 64° Fahr. as 
before. 
At thirty minutes, that is to say, as soon as the water was added, the chamber was 
in three eggs largely developed, as much as it would have been in an hour in eggs 
only moderately supplied with spermatozoa, though in the fourth egg the degree was 
not quite so great. From eight to twelve spermatozoa were detected in each chamber, 
and some motionless in the fluid ; others on the vitelline membrane had their serpen- 
tine movements ; and others were projecting from the membrane motionless, as if 
their force had been expended before they could effect an entrance. 
This last experiment seems to favour my view, that the changes in the yelk are 
hastened by excess of the fecundating fluid. 
From the facts stated above, and before detailed in my former papers, the con- 
clusion seems to be arrived at, that the fructifying of the egg depends on the force or 
power residing in the sperm body to make its way through the thick coverings of the 
yelk ; and that, this being the case, an explanation will be afforded of the failure of 
the fluid to occasion fecundation when those bodies are deficient in number or well- 
being, or are deprived of the power of moving: and at the same time the penetrating 
power may afford a clue to the inability of filtering paper, even when it is twice or 
thrice folded, to stop their progress through it. 
The action of the spermatozoon is influenced by the temperature of the air, and by 
mechanical impediments to its passage into the egg. 
With respect to temperature, I have frequently referred to its influence in expe- 
diting or retarding the development of the embryo, and the following general 
statement may be given in support of it. A given number of eggs, at a mean 
temperature of 61° Fahr., will advance in four days as far as a corresponding set, at 
a mean temperature of only 47° Fahr., will reach in fourteen days. Further, the 
embryos exposed to the low temperature mentioned above die and decompose, whilst 
mdcccliv. 2 H 
