SECOND LECTURE. 



THE FERTILIZATION OF THE OVUM. 



E. G. CONKLIN. 



IN the history of the biological sciences perhaps no problem 

 has received more attention than the fertilization of the ovum. 

 The first important advance in our knowledge of this phe- 

 nomenon within recent years was made by O. Hertwig 1 about 

 twenty years ago. He showed that after a period of prepara- 

 tion in which the egg cell extrudes two small corpuscles, the 

 polar bodies, the nuclei of the male and female cells fuse to 

 form the first or segmentation nucleus of the new organism. 

 He therefore held that the process of fertilization consisted 

 essentially in the fusion of two nuclei coming from different 

 individuals. 



This idea has dominated biology for the past decade, and it 

 is the generally accepted view to-day. In his recent work, Die 

 Zelle und die Gewebe, Hertwig says (p. 220), "The nuclear sub- 

 stances which are derived in equal quantities from two different 

 individuals, are the only essential substances upon whose union 

 the act of fertilization depends ; they are the real fertilization 

 materials. All other substances, such as protoplasm, yolk, 

 nuclear sap, etc., have nothing to do with fertilization as such." 

 It is well known that Weismann in his various essays and 

 works upon heredity has expressed himself as fully satisfied 

 that the essence of fertilization consists in the fusion of the 

 nuclei of the ovum and spermatozoon. In fact his whole 

 theory is to a very large extent founded upon this fundamental 

 assumption that fertilization is essentially a nuclear process. 

 And quite recently Boveri, 2 after a full discussion of the ques- 



1 O. Hertwig, Beitrage zur Kenntniss der Bildung, Befruchtung und Theilung 

 des thierischen Eies. Morphol. Jahrbiicher^ 1875, 1877, 1878. 



2 Boveri, Befruchtung. Ergebnisse der Anatomic it. Entwick,, 1892. 



