THE OVUM IN THE AMPHIBIA. 205 



No. 6. Thirty drops of Jittered fluid were added to one ounce of water with two 

 hundred and ten ova. At the expiration of five hours two ova had become segmented, 

 and two embryos were afterwards produced. 



No. 7. Thirty drops of diluted fluid, notjiltered, were added to water with two hun- 

 dred andjifty ova. At four hours and forty-two minutes segmentation had commenced 

 in two or three of these, and in Jive hours had occurred in almost every ovum. Nearly 

 the whole of these produced embryos. 



No. 8. About thirty drops of the same diluted fluid, notjiltered, were added to 

 water that contained about two hundred ova, passed from the body of a frog killed 

 twenty hours before. A few of these ova became imperfectly segmented, but not 

 one produced an embryo. 



From these first experiments with filtered fluid, it seemed that the portion of semen 

 which passes through the filter has not the power of impregnating, unless there are 

 spermatozoa present in it ; while similar quantities of diluted semen that has not been 

 filtered, are efficient and impregnate, as in Nos. 4, 5, 6 and 7- Further, it is shown, 

 from No. 8, if we may judge from one experiment, that ova which have remained in 

 the body of a frog twenty hours after actual death and cessation of the organic func- 

 tions, and in a temperature of 55 FAHR., may be affected by the stimulus of the im- 

 pregnating fluid, but not sufficiently so perhaps as to result in fruitful impregnation. 



During the time these ova were under observation, in March 1849, an opportunity 

 occurred of observing the effect of reduced temperature on the rate of development 

 of the embryo when its formation has been somewhat advanced. On the seventh, 

 eighth and ninth days after impregnation of the ovum, and when the temperature 

 had already been considerably reduced, the season became severe, and in order to 

 test the effects of cold, the eggs were removed to the open air and exposed to a keen 

 wind. The temperature of the atmosphere was then 38 FAHR. During the night of 

 the tenth day, the water in which the ova were contained was frozen to a mass of ice. 

 Yet many of these ova, as above shown, produced embryos. SPALLANZANI had already 

 remarked, that the eggs of the Frog may be inclosed in ice, and yet afterwards pro- 

 duce embryos, if the envelope does not become frozen*. 



The experiments made to ascertain whether cleavage of the yelk may be taken as 

 a test of impregnation (p. 190), seemed also to show that, within certain limits, a 

 large or small quantity of seminal fluid has some influence on the more or less early 

 occurrence of this phenomenon. It occurred to me, therefore, that in making the 

 experiments now given, two questions might be examined : one, as to whether the ex- 

 tremely minute quantities of seminal fluid disseminated in water, as mentioned by 

 SPALLANZANI, are as efficient to produce the embryo at the low temperature of the 

 season at which the Frog spawns in this country, as in the warmer region of 

 Italy; and the other, whether the presumed efficiency of such minute quantities de- 

 pended on the presence of the spermatozoa ; and it seemed possible to put these 



* Dissertations, &c., vol. ii. p. 49. 



