THE OVUM IN THE AMPHIBIA. 227 



No. 3. P.M. l h 50 m . Forty-seven ova were passed on a dry surface, and spermatic 

 fluid was instantly applied to them, and within ten seconds afterwards the ova were 

 washed with the solution of potass, which was allowed to remain, and water was then 

 added. At the end of the eighth day not a single embryo had been produced. The 

 difference between this experiment and the above was the non-removal of the potass, 

 and the more free bathing of the ova. 



No. 4. P.M. l h 53 m . Forty-jive ova were passed on a dry surface, and werejirst 

 bathed with solution of potass, and then with seminal fluid in water, and afterwards 

 they were removed with No. 1 and 2, to higher temperature. 



At the expiration of the eighth day three embryos had been formed. This result at 

 first appeared to be more difficult of explanation than the former. But, when the 

 circumstances are considered, it seems to admit of quite as easy an interpretation. 

 The bathing of the ova freely with seminal fluid mixed with water,^e seconds after 

 the application of the solution of potass, diluted this solution too much to allow of 

 its effect on the whole of the spermatozoa applied to the ova, while this very dilution 

 enabled the impregnating influence of these bodies to take effect in some of the ova. 

 The fact, however, leads to an inference of some importance with reference to the 

 action of the potass on the envelopes of the ovum, and seems to show that this 

 action is less immediate on the envelopes than on the spermatozoa. 



No. 5. Fifty-nine ova were bathed with seminal fluid and water, and Jive seconds 

 afterwards with a solution of nitrate of potass (in the proportion of twenty grains of 

 the salt to one ounce of water), and water was then added to them. 



No. 6. Seventy-two ova were treated in precisely the same way. 



Not one embryo was produced in either of these experiments. 



No. 7- Forty-four ova were washed with diluted acetic acid immediately after they 

 had been shed from the female, and^we seconds afterwards, seminal fluid with water 

 was added to them. 



No. 8. Seventy-six ova were washed with diluted acid, and treated in every way as 

 in No. 7- 



Not a single embryo was produced in either of these trials. 



The action of acetic acid is almost instantaneous on the envelope of the ovum, 

 which it quickly contracts, and renders slightly opaque. 



Besides those media which act chemically on the spermatozoa and the ova, I 

 made trial, in this and the two following sets of experiments, with a solution of gum- 

 arabic, the effect of which appears to be entirely mechanical ; and as the results are 

 curious and seemingly important with reference to the nature of the agency of the 

 spermatozoa in impregnation, I defer the mentioning of them until I have to show 

 the effect of media which operate mechanically on the ovum or the spermatozoon in 

 impregnation. 



The result of the preceding experiments was so remarkable, that it seemed necessary 

 that they should be repeated with greater precision, with reference to exact periods 



2 G 2 



