252 MR. NEWPORT ON THE IMPREGNATION OF THE OVUM IN THE AMPHIBIA 



first experiment, made on the 5th of April, with fluid which had been mixed with 

 water about one hour and Jifty minutes before, twelve eggs contained in a single cell 

 were each twice or thrice freely touched with the loaded pin's-head over the centre 

 of the white surface. Three of these eggs became partially impregnated, as shown 

 in the formation of the chamber in each, and segmentation commenced in one of 

 them, but no embryo was produced from either. Fourteen eggs in another cell were 

 touched at the same time, and in the same way as the preceding, with the loaded 

 pin's-head, over the centre of the black surface of the yelk. The whole of these eggs 

 produced healthy and well-formed embryos. 



These experiments were repeated on the following day on the eggs of another frog, 

 with fluid which had been obtained only about twenty minutes before it was employed. 

 Fourteen eggs were each touched once only on the centre of the white surface, the 

 pin-head being loaded for each egg. But not one of these eggs became fecundated, 

 nor was even one of them partially impregnated. In another cell, at the same time 

 with these, thirteen eggs were touched on the centre of the dark surface, and four of 

 them became partially fecundated, but only two embryos were produced. The failure 

 in this experiment certainly appeared to be due to the eggs, rather than to the mode 

 of attempting their fecundation. 



At the time of making this experiment I placed two eggs, each in a separate cell, 

 with their white surface uppermost, and then filled the cells, the one with nearly pure 

 fluid, and the other with equal parts of fluid and water. Each of these eggs became 

 fecundated, and underwent segmentation, although more slowly than usual, but the 

 development of their embryos was not completed, as it became arrested at a parti- 

 cular period, a circumstance which is presently to be explained. Yet these experi- 

 ments showed that when the egg is completely immersed in fluid its position at the 

 moment has but little reference to the act of fecundation, provided the fecundatory 

 agents are present in good abundance. A further trial was made on the 9th of April, 

 when six eggs, placed in one cell, were each twice touched on their white surface, the 

 pin's-head being loaded each time it was employed. But neither of these eggs pro- 

 duced an embryo. Six eggs, placed in another cell, were also twice touched, like the 

 preceding, on their dark surface. The whole of these eggs became fecundated, but 

 only Jive embryos were sufficiently matured as to leave their envelopes. The fluid 

 employed in these two experiments had been mixed with water about Jifty-Jive minutes 

 before it was applied to the eggs, and consequently was becoming slightly deterio- 

 rated. 



The conclusion which seems to be deducible from a comparison of these experi- 

 ments is, that when the egg of the frog is completely immersed in water charged 

 with the fecundatory agents, or to which these are supplied quickly after the immer- 

 sion of the egg, as in the natural fecundation of the species, the actual position of the 

 egg at the moment of its encounter with the spermatozoon, has but little reference 

 to the act of fecundation, every part of its surface having then an equal chance of 



