THE OVUM IN THE AMPHIBIA. 
201 
perature in which they had been retained being 59°"5 Fahr. On the eighth day, when, 
as already shown, the thirteen embryos of No. 1 H had left the egg, only three had 
been developed in this set of observations. No. 1 I, and these had reached only to the 
commencement of the formation of the laminse dorsales, the mean temperature of 
the room during the entire period being then advanced to 45°72 Fahr.; and the 
completion of their third phase of development did not take place until the tenth or 
eleventh day. 
Thus while three embryos only were produced in this experiment. No. 1 I, during 
exposure to light and at a mean temperature now raised to 47°‘38 Fahr., thirteen 
in No. 1 H were developed in about one-half the space of time from a similar number 
of eggs removed from the light, and at a mean temperature of 59°'5 Fahr. ; so that 
we seem here to have good reason to believe that a low temperature of the medium 
not only retards the development of the embryo, even when exposed to light, but 
injuriously affects the fecundation of the ovum. 
The result of the next experiment coincides with the above. 
No. 2. p.M. 1^56“. — Fifty-one om were touched in the same way with spermatozoa 
from the filter paper, as in No. 2 H, and were retained in the same temperature as 
the preceding. 
A few of the yelks became ovoid in about six hours, but segmentation did not com- 
mence until seven hours and two minutes, and then only in a very few. Two embryos 
only were produced from this set. 
No. 3. p.M. 2^’ 5“. — Fifty-five ova were bathed with filtered fluid in exactly the 
same way as in No. 3 H ; but not a single ovum became segmented. Not one pro- 
duced an embryo. 
Thus while segmentation took place in No. 1 H, in three hours and fifty-six minutes, 
when the temperature was rising from 59° Fahr. to 64° Fahr., it did not occur in 
No. 1 I, until seven hours and forty-five minutes, when the temperature during the 
interval was sinking from 48° Fahr. to 47° Fahr. This sufficiently marks the great 
influence of temperature during the earliest periods of change in the ovum ; and this 
injurious effect of reduction of temperature at that period is further shown in the 
relative number of embryos in these comparative experiments. That the injurious 
effect of reduced temperature at the time of impregnation is mainly the cause of this 
result, and not the diminution of temperature after the period of impregnation, seems 
to be shown in the circumstance, that while at the end of the eighteenth hour the ova 
in the set H had already passed through all the stages of segmentation, and the 
surface of the yelk had become granulated, and the blastoderma had begun to be 
formed even although the temperature in that case subsided a little after segmen- 
tation had commenced, — from 59° to 57°, — the corresponding set of ova. No. 1 I, had 
advanced only to the octuple division of the yelk. A similar difference in the rate 
of development we have seen takes place in the growth of the embryo. At the end 
of three days the embryos of set H were advanced to the stage at which the laminse 
2 D 
MDCCCLI. 
