216 W. WALDEYER. 
matozoon which penetrates into the egg, and the nucleus 
(reduced in a peculiar way) of the ripe egg-cell. 
The historical development of our knowledge of this very 
important process may be here briefly reviewed. All those 
who, like Purkyne (164), von Baer (6, 7), Oellacher (150), 
Gotte (80), Reichert (169), Kleinenberg (104), Lovén (128), and 
others, supposed the whole of the germinal vesicle, together 
with the germinal spot, to disappear before fertilization, must 
naturally have looked upon the essence of the process of ferti- 
lization quite otherwise than as a morphological copulation 
between the spermatozoon and the germinal vesicle. There 
were, however, not a few earlier workers who recognised the 
germinal vesicle as persistent. Thus, Joh. Miller’s (142) 
observations on the mollusc Entoconcha mirabilis, will 
always be quoted as a classic example. Associated with him are 
Leydig (124, 125), Gegenbauer (75, 76), and above all HE. van 
Beneden, in his great memoir on the egg (“ Recherches sur la 
composition et la signification de l’euf,’ ‘Mém. couronné de 
VAcad. roy. des Sci. de Belgique,’ Bruxelles, 1870). By most 
of these writers it was, however, held that the persistent ger- 
minal vesicle, even before the beginning of its subdivision by 
segmentation, differed more or less from its earlier condition. 
Thus, many believed the germinal spots to disappear; but we 
also find statements (Kolliker (106), Gegenbauer (76), Haeckel 
(85), and specially EH. van Beneden, in regard to Distomum 
cygnoides) to the effect that the germinal vesicle and spot 
remained intact till division occurred. Fol (“‘ Recherches sur la 
fécondation et le commencement de l’hénogénie chez divers 
animaux,” ‘ Mém. de la Soc. de phys. et d’hist. nat. Genéve,’ t. 
xxvi, 1878, 1879) carefully figured the preliminary change in 
the germinal vesicle preceding fertilization. Finally, a third 
view is taken by the following authors :—Derbés (55), von 
Baer, Leydig, Bischoff (27, 28), Fol (65), viz. that in certain 
examples the germinal vesicle disappears, although the germinal 
spot remains. Certainly Derbés speaks positively on this 
point ; the rest are very reserved. Bischoff has lately quite 
withdrawn from this yiew. O. Hertwig (98) agreed with Derbés’ 
