AUGUST WEISMANN 353 



process. There must be some cause for this separation, and I have 

 already tried to show that it may He in the quantitative relations which 

 obtain between the two kinds of nucleoplasm contained in the nucleus 

 of the egg. I have suggested that the germ-plasm, at first small in 

 quantity, undergoes a gradual increase, so that it can finally oppose the 

 ovogenetic nucleoplasm. I will not further elaborate this suggestion, 

 for the ascertained facts are insufficient for the purpose. But the 

 appearances witnessed in nuclear division indicate that there are op- 

 posing 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 ef- 

 fects 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 

 capable 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 fertiliza- 

 tion has been represented as analogous 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 repulsion manifested in the nuclear division 

 which immediately follows fertilization, to the antagonism between 

 male and female elements. But, according to the important discov- 

 eries 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 through- 

 out the whole ontogeny. 



