1 6 BIOLOGICAL LECTURES. 



tion, concludes with these words r 1 "Their union [that of the 

 egg and sperm nucleus] is not the condition but the goal of 

 fertilization, and in this sense the statement is true to-day in 

 which O. Hertwig summed up the results of his first funda- 

 mental investigations, that 'the essential thing- in fertilization is 

 the union of egg and sperm nucleus! ' 



It is only within the most recent times that a different view 

 has arisen, and for the sake of clearness I will sketch briefly 

 the rise of the idea that fertilization is not a purely nuclear 

 phenomenon, that it does not consist simply in a union of 

 nuclei coming from different individuals, but rather, as it seems 

 to me, in a union of all the essential parts of the reproductive 

 cells, cytoplasm as well as nuclei. 



In 1873 Hermann Fol 2 described in the eggs of a jelly-fish 

 two star-shaped figures or asters at the two poles of the 

 nucleus, and one year later E. Van Beneden 3 described a 

 polar corpuscle as present in the cytoplasm during the karyoki- 

 netic division of the nucleus in some small parasitic organisms, 

 the Dicyemidae ; but it was certainly not until a much later 

 date that anything satisfactory was known of these bodies. 



In 1887, only six years ago, Van Beneden 4 in his work on 

 the fertilization of the egg of Ascaris, a thread-worm inhabit- 

 ing the intestine of the horse, gave a very minute account 

 of two granular bodies, the spJieres attractives which he 

 believed to be present at all times in the cytoplasm of the cell. 

 He described -each sphere as consisting of a central refractive 

 body, the central corpuscle, around which was a clear space, the 

 medullary zone, which in turn was surrounded by a deeply 

 staining granular area, the cortical zone, Fig. i, A and C. 

 Although he regarded these spheres as permanent organs of 

 the cell, he did not know how they originated in the egg under- 

 going fertilization, but he thought that the two spheres appeared 

 simultaneously in the egg as newly formed structures, and he 



1 Loc. cit., p. 433. 



2 Hermann Fol, Die erste Entwicklung cles Geryonideneies. Jenaische Zeit- 

 schrift, 1873. 



3 E. Van Beneden, Recherches sur les Dicyemides. Bull. Acad. roy. Belg., 1874. 



4 Van Beneden et Neyt, Nouvelles Recherches sur la Fecondation et la Division 

 mitosique chez 1'Ascaride megalocephale. 



