THEIE SIGNIFICANCE IN HEREDITY. 361 



plasms into halves is inconceivable ; and because the first polar 

 body is also present in parthenogenetic eggs in which such division 

 into halves cannot take place. But the karyokinetic process can 

 readily be looked upon as a removal of ovogenetic nucleoplasm, for 

 we know from the observations of Flemming and Carnoy, that, 

 under certain circumstances, subsequent divisions may occur, in- 

 volving an increase in the number of nuclear loops to double their 

 number. These subsequent divisions of course take place in the 

 daughter-nuclei. This fact proves, as I think, that there are nuclei 

 in which the same ancestral germ-plasm occurs in two different 

 loops : but such loops, identical as regards the composition of their 

 ancestral germ-plasms, may very well contain different ontogenetic 

 stages of this substance. This will be the case in the instance 

 alluded to, if four loops of the first nuclear spindle are to be looted 

 upon as ovogenetic nucleoplasm, and the four others as germ- 

 plasm. It is therefore unnecessary to regard the first division of 

 the egg-nucleus as a ' reducing division ' : it may be looked upon as 

 an 'equal division n entirely analogous to the kind of division which, 

 in my opinion, directs the development of the embryo. This con- 

 clusion would receive direct proof if it were possible to show that 

 the eight loops of the first division have arisen by the longitudinal 

 splitting of four primary loops : for a longitudinal splitting of the 

 nuclear thread would be the means by which the different onto- 

 genetic stages of the germ-plasm could be separated from one 

 another, without leading to any reduction in the number of ances- 

 tral germ-plasms in the daughter-nuclei. Thus I have previously 

 attempted to prove that the ontogenetic development of the egg 

 must be connected with a progressive transformation of the nucleo- 

 plasm during successive nuclear divisions, and this transformation 

 will very frequently (but not always) occur in such a way that the 

 different qualities of the nucleoplasm are separated from one another 

 by the nuclear division. The nucleoplasm of the daughter-nuclei 

 will be identical if the two daughter-cells are to potentially contain 

 corresponding parts of the embryo ; as for instance the first two 

 segmentation spheres of the egg of the frog, which according to 

 Roux 2 correspond to the right and left halves of the future animal. 



1 See p. 364. 



2 Wilhelm Koux, 'Beitriige zur Entwicklungsmechanik des Embryo,' No. 3, 

 Breslauer arztllche Zeitschrift, 1885, p. 45. 



