972 



the agency of the spermatozoon has thus remained open ; and it is 

 to this question, with a view first to supply proof from direct expe- 

 riments of the fact of the agency of this body, as well as to examine 

 into the circumstances under which this agency is exerted, influenced 

 or impeded, that the present communication is especially devoted. 



The author then traces the changes in the ovum within the body 

 of the Amphibia, from a short time before the disappearance of the 

 germinal vesicle to the period when the ovum is expelled before 

 impregnation. The structure of the germinal vesicle in the ovarian 

 ovum is shown to be an involution of cells, as stated by Wagner 

 and Barry ; but the author differs entirely from the latter respecting 

 the mode of disappearance of the vesicle, and also respecting the 

 part played by its constituents in the production of the embryo. 

 He believes the included cells are liberated by the diffluence of the 

 membrane of the germinal vesicle in the interior of the yelk, not in 

 the centre of the yells, but much nearer to the upper or dark surface 

 than to the white or inferior, and at the bottom of a short canal, the 

 entrance to which is in the middle of the upper or black surface at 

 a point already noticed by Prevost and Dumas, Rusconi and Boa; 

 and he thinks that it is due to the diffluence of the envelope of the 

 vesicle in this situation that the moment of disappearance has not 

 yet been observed. The germinal vesicle in the Amphibia always 

 disappears before the ovum leaves the ovary, and escapes into the 

 cavity of the abdomen. The mode in which the ovum, after leaving 

 the ovary, is believed to arrive at the entrance of the oviduct is then 

 stated, and the structure of the entrance in the intermedial space, 

 as shown by Swammerdam, described. 



The author then traces the changes in the impregnated and in 

 the unimpregiiated ovum after spawning, from the first minute to 

 the segmentation of the yelk in the former, and shows that the ap- 

 pearances in the two are almost identical during the first ten or 

 twelve minutes, but that after that time the changes in the unim- 

 pregnated ovum cease, while further changes take place in the im- 

 pregnated. The yelk at the end of from twelve to fifteen minutes 

 invariably then rotates, so that the dark surface becomes uppermost ; 

 and it constantly afterwards returns to this position, however much 

 or frequently this may be changed. In about three hours the yelk 

 becomes separated on the upper surface from the vitelline mem- 

 brane, and a space or chamber is formed between the two. The 

 yelk then becomes depressed on the upper surface, but is slightly elon- 

 gated to an obtuse oval form, in the horizontal direction ; and in 

 about half or three-quarters of an hour afterwards begins to divide 

 in the margin of the central spot or orifice, from which point the 

 division, as already known, passes outwardly and around the yelk 

 until the mass is divided into two portions. These changes do not 

 take place in the unimpregnated ovum, which merely becomes some- 

 what oval, but does not divide ; so that segmentation may be re- 

 garded as a proof that the egg has been impregnated, a fact that 

 was of great use as a test in the following experiments. The sus- 

 ceptibility of the ovum to become impregnated, and the circum- 



