FOUNDATION OF A THEORY OF HEREDITY. 231 



so that it can finally oppose the ovogenetic nucleoplasm. I will not 

 further elaborate this suggestion, for the ascertained facts are in- 

 sufficient for the purpose. But the appearances witnessed in nuclear 

 division indicate that there are opposing forces, and that such a 

 contest is the motive cause of division ; and Roux * may be right 

 in referring the opposition to electrical forces. However this may 

 be, it is perfectly certain that the development of this opposition 

 is based upon internal conditions arising during growth in the 

 nucleus itself. The quantity of nuclear thread cannot by itself 

 determine whether the nucleus can or cannot enter upon division ; 

 if so, it would be impossible for two divisions to follow each other 

 in rapid succession, as is actually the case in the separation of 

 the two polar bodies, and also in their subsequent division. In 

 addition to the effects of quantity, the internal conditions of the 

 nucleus must also play an important part in these phenomena. 

 Quantity alone does not necessarily produce nuclear division, or the 

 nucleus of the egg would divide long before maturation is complete, 

 for it contains much more nucleoplasm than the female pronucleus, 

 which remains in the egg after the expulsion of the polar bodies, 

 and which is in most cases incapable of further division. But the 

 fact that segmentation begins immediately after the conjugation of 

 male and female pronuclei, also shows that quantity is an essential 

 requisite. The effect of fertilization has been represented as ana- 

 logous to that of the spark which kindles the gunpowder. In the 

 latter case an explosion ensues, in the former segmentation begins. 

 Even now, many authorities are inclined to refer the polar repul- 

 sion manifested in the nuclear division which immediately follows 

 fertilization, to the antagonism between male and female ele- 

 ments. But, according to the important discoveries of Flemming 

 and van Beneden, the polar repulsion in each nuclear division is 

 not based on the antagonism between male and female loops, but 

 depends upon the antagonism and mutual repulsion between the 

 two halves of the same loop. The loops of the father and those 

 of the mother remain together and divide together throughout 

 the whole ontogeny. 



What can be the explanation of the fact that nuclear division 

 follows immediately after fertilization, but that without fertilization 



1 W. Roux, ' Ueber die Bedeutung der Kerntheilungsfiguren.' Leipzig, 1883. 



