THE OVUM IN THE AMPHIBIA. 229 



sixty, and there were nine also which became shrivelled and decayed. Notwithstand- 

 ing the great proportion of ova segmented, not one produced an embryo. 



No. 4. P.M. 5 h . Sixty-six ova, passed on a dry surface, were bathed as in No. 2, 

 with impregnating fluid, and one second afterwards were washed quickly with strong 

 solution of potass, and water was then added ; the period occupied being sixty-two 

 seconds. 



Only two ova became segmented, while, excepting only eight or nine ova, the whole 

 of the remainder were shrivelled, irregular, or compressed in form, and distinctly 

 spoiled, apparently by the action of the potass, thus showing that endosmose and 

 exosmose through the envelopes had taken place. 



No. 5. P.M. 4 h 55 m . Fifty -four ova were passed, and washed with the weak solution 

 of potass, and afterwards, at an interval of two seconds, with impregnating fluid and 

 water, and water was then added and allowed to remain. The whole time occupied 

 was Jifly seconds. 



One ovum only became segmented ; but several others had slightly altered their 

 form to the obtuse oval, as if about to become divided : no embryo was produced. 



No. 6. P.M. 5 1 ' 2 m . Seventy-nine ova were washed with strong solution of potass, 

 and one second afterwards with impregnating fluid, and water was then added. 



Not one ovum became segmented, nor did even one yelk retain its proper shape. 

 The whole were irregular and spoiled. Five ova had the envelope clouded and opaque, 

 and the surface of others was translucent with refracted light, like crystallized car- 

 bonate of lime. In one egg only had there been any attempt at segmentation. This 

 experiment, like No. 4, seemed to show that the act of expansion of the chorion is 

 an act of endosmose. 



No. 7. P.M. 5 h 15 m . Nitrate of Potass. Seventy-seven ova were passed on a dry 

 surface, and were well bathed with impregnating fluid in water, and one second after- 

 wards with a weak solution of nitrate of potass, and water was then added to them ; 

 the whole time occupied being thirty seconds. 



Segmentation took place in forty-three of these ova, and the whole retained their 

 natural form and size. The effect of the nitrate of potass, as compared with the 

 caustic solution, was thus very marked, as showing that the momentary application 

 of the nitrate does not prevent or arrest impregnation in weak solution (eight grains 

 to one ounce of water), even when applied after the impregnating influence. The 

 experiment was also interesting in another respect. It proved that the ova were sus- 

 ceptible of being impregnated, and that the fluid from the testes was efficient to 

 induce the first evidences of impregnation. But none of these ova, or of the ova in 

 the preceding experiments of this set, produced embryos. Subsequent observations 

 will show that this failure was not due to the nitrate of potass, but perhaps was at- 

 tributable to the conjoint causes of low temperature at the time of impregnation, and 

 of some imperfection both in the seminal fluid and the ova. 



No. 8. P.M. 5 h 9 m . Seventy-six ova were washed with diluted acetic acid as in Set P, 



