MEMOIRS. 



On the Phenomena accompanying the Maturation and 

 Impregnation of the Ovum. Bj P. M. Balfour, M.A., 

 Pellow of Trinity College, Cambridge. 



The brilliant discoveries of Strasburger and Auerbach have 

 caused the attention of a large number of biologists to be turned 

 to the phenomena accompanying the division of nuclei and the 

 maturation and impregnation of the ovum. The results of the 

 recent investigations on the first of these points formed the sub- 

 ject of an article by Mr. Priestley in the sixteenth volume of this 

 Journal, and the object of the present article is to give some 

 account of what has so far been made out with reference to the 

 second of them. The matters to be treated of naturally fall 

 under two heads : (1) the changes attending the ripening of the 

 ovum, which are independent of impregnation ; (2) the changes 

 which are directly due to impregnation. 



Every ovum as it approaches maturity is found to be 

 composed (Fig. 1) of (1) a protoplasmic body or vitellus usually 

 containing yolk-spherules in suspension; (2) of a germinal 



Fig. 1. — Unripe ovum of Toxopueustes lividus (copied from Hertwig). 



vesicle or nucleus, containing (3) one or more germinal spots or 

 nucleoli. It is with the germinal vesicle and its contents that we 

 are especially concerned. This body at its full development has a 

 more or less spherical shape, and is enveloped by a distinct mem- 



VOL. XVIII. NEW SER. H 



