THE OVUM IN THE AMPHIBIA. 
197 
became fully impregnated or afterwards produced an embryo. In two or three ova 
there were slight indications of partial impregnation. 
No. 5. p.M. 12^ 37“. — Sixty -jive ova having remained Jifteen minutes in water', were 
exposed, and thoroughly bathed with impregnating fluid applied with a hair-pencil, 
Jifty-one minutes after it had been obtained, and water was then added to them. Seg- 
mentation did not take place in these ova. 
No. 6. p.M. 12^ SS*”. — Seventy-seven ova, passed into a solution of carmine ior jifteen 
minutes, were exposed, and thoroughly bathed with impregnating fluid as in No. 5, 
and water was then added ; but not a single egg gave any sign of impregnation. 
Influence of Temperature. — From these experiments, it seemed evident that the 
susceptibility of the ovum to become impregnated is diminished in proportion to the 
degree of expansion of its envelope and its imbibition of fluid, conditions which are 
greatly affected by the temperature of the medium in which the ovum is placed during 
the first hour; and there seems reason to suppose that this diminution may be due to 
the extent to which the envelope becomes influenced by temperature, rather than to 
any insusceptibility at that time in the yelk itself. The following experiments, made 
a few hours after the above, tend to support this view. 
Set G. March 22, 1850. Atmosphere 48° Fahr. Water 47°. 
No. 1. p.M. 4'* 30“. — Fifty-eight ova were passed from the female from which the 
ova used in the preceding experiments were obtained, four hours and a half after 
division of the spinal cord ; and seminal fluid mixed with W'ater, and obtained jifteen 
minutes before, was immediately added to the water in which they were immersed. 
The ova were removed at the end of twenty-five minutes to a room in which the 
temperature was then 62° Fahr. Segmentation took place in almost every ovum a 
few minutes within the sixth hour, at which time the temperature of the air was 64° 
Fahr., and that of the water 62°. At the eighth ddiY,jifty-three out of fifty-eight ova 
had produced embryos. 
No. 2. p.M. 5’’. — Sixty-three ova from the same female were well bathed with im- 
pregnating fluid, and water was then added to them. The fluid in this case had been 
obtained three quarters of an hour. Segmentation took place in the majority of these 
at the end of Jive hours and a half 
No. 3. March 23. p.m. 12'' 45®. — One hundred and twenty-four ova from the same 
female, twenty-four hours after section of the spinal cord, were passed into water, 
and impregnating fluid soon after it was obtained supplied to them. The ova were 
placed in a temperature of about 60°, and nearly the whole produced embryos. 
These facts proved that the ova employed were still fitted to become impregnated 
when the fluid was supplied to them in sufficient abundance, and for a sufficient length 
of time, and within the period during which the envelope continues to expand and im- 
bibe most rapidly. This condition is always promoted by an early removal from a 
low to a comparatively high temperature during the period of expansion, as in Set G, 
in which segmentation took place in from jive hours and a half to six hours, and when 
