THE OVUM IN THE AMPHIBIA. 201 



perature in which they had been retained being 59 0< 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 4572 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. I h 56 m . Fifty-one ova 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 h 5. Fifty-jive 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 FAHH., 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 

 MDCCCLI. 2 D 



