GERMINAL VESICLE AND FIRST EMBRYONIC NUCLEUS. 171 



inent with osmic acid, the nuclear substance is stained of a 

 rose colour ; the nucleolus and the membrane bright red ; 

 the reticular substance does not stain. This is also the case 

 with the nucleo-plasmic meshwork of the germinal vesicle of 

 the rabbit. 



But if one opens the ovary of the starfish at the moment 

 of sexual maturity one finds in it not only ova similar to 

 those which I have just now described, and which are essen- 

 tially distinguished by the fact that although they have 

 attained the dimensions of the ripe ovum they still have their 

 germinal vesicle in the centre of the vitellus ; together with 

 these ova one sees others which have not yet attained 

 maturity ; others in every respect similar to those of 

 which I have before spoken, but differing from them in the 

 fact that the germinal vesicle has become superficial ; and 

 others which show no longer any trace of the vesicle of 

 Purkinje. These latter, however, are ova which are only 

 exceptionally observed ; generally speaking, all the ovarian 

 ova still possess their germinal vesicle. 



The ova in which the germinal vesicle has reached the 

 surface of the yolk scarcely diifer from those above described ; 

 they have an ellipsoidal or spheroidal form ; their zona 

 pellucida,. swollen by the seawater, is very thick, and its 

 surface quite irregular. The yolk invariably presents the 

 same characters ; the germinal vesicle has retained its 

 spherical form, and all the sharp definition of its contour. 

 It is difficult to make out whether it is in immediate contact 

 with the zona pellucida, or whether it is separated from that 

 membrane by a thin layer of vitelline protoplasm. Inside 

 the vesicle are seen the nucle'iis and pseudo-nucleoli in the 

 midst of a little cluster of granules. I have never found the 

 nucleo-plasmic network in the germinal vesicle when it has 

 become superficial, whatever the method to which I have had 

 recourse to convince myself of its presence. From the time 

 when the germinal vesicle has taken its peripheral and 

 superficial position, the nucleo-plasma, together with the 

 pseudo-nucleoli, forms a small nucleo-plasmic mass by the 

 side t-f the nucleolus. 



If the ovarian ova of a completely developed ovary are 

 received into a small vesicle containing sea-water, and if a 

 fragment of testicle which has reached maturity be shaken 

 in it for a moment, a certain number of ova are fecundated, 

 and two or two and a half hours after having performed the 

 artificial fecundation, divided ova are found at the bottom of 

 the vessel. If one has taken care to leave only a small 

 number of ova in the vessel, aad to renew the water from 



