THE OVUM IN THE AMPHIBIA. 



195 



minutes, were then exposed, well-bathed with impregnating fluid, and water imme- 

 diately added to them. The fluid employed had been obtained twenty-six minutes. 

 Segmentation commenced in four hours and fourteen minutes, but was more general 

 in four hours and seventeen minutes. On the eighth day there were forty-Jive em- 

 bryos. 



No. 8. P.M. 2 h 24. About one hundred ova were submerged for half an hour, and 

 impregnating fluid obtained forty four minutes before was then supplied to them, but 

 not more than six or eight ova became segmented, and only two embryos were formed. 



The following summary will more immediately indicate the results: 



TABLE I. Set E. 



Thus then at a temperature of 60 FAHR. the susceptibility of the ovum to become 

 impregnated is greatest at the time it is passed into water, and for two or three 

 minutes afterwards, and segmentation then takes place more quickly, even when the 

 seminal fluid has been for nearly three quarters of an hour mixed with water, than 

 after longer immersion. The fitness of the ovum to become impregnated is gradually 

 diminished, and segmentation takes place more tardily, according to the length of 

 time which the ovum has remained in water, as is seen by comparing the results of 

 Nos. 1 and 2 with 7 and 8. On the other hand, while the desiccating effect of expo- 

 sure to air more arrests the fecundation of the ovum and the occurrence of segmenta- 

 tion of the yelk than a continuance for a corresponding length of time in water, it 

 seems to be less prejudicial to the fecundity of the ovum than immersion in that fluid, 

 as appears to be shown by comparison of Nos. 4 and 6 with 3 and 5, the difference 

 in the number of ova produced being too great to lead us to attribute this to differ- 

 ence in the length of time the impregnating fluid had been obtained. 



In the foregoing set of experiments, the quantity of impregnating fluid supplied to 

 the ova was but little attended to, it being added very freely in each case. In the 

 following set I was desirous of knowing what difference would result from the fluid 

 being applied more sparingly, or but for a very short space of time. SPALLANZANI 

 had made experiments with a similar view, but his appeared to be open to some ob- 

 jections, as he had not noted some important circumstances which greatly affect 

 the result, as the temperature of the medium, the length of time the fluid employed 

 had been obtained, &c. In the experiments now made, these circumstances were 



2 c 2 



