VI.] THEIR SIGNIFICANCE IN HEREDITY. ^J^ 



of the egg of the frog, which according to Roux ^ correspond 

 to the right and left halves of the future animal. But the 

 nucleoplasm must be unequal if the products of division are to 

 develope into different parts of the embryo. In both cases, 

 however, karyokinesis is connected with a longitudinal splitting 

 of the nuclear threads, and we may conclude from this fact 

 (which is also confirmed by the phenomena of heredity) that 

 all such nuclei, whether they have entered upon the same or 

 different ontogenetic transformations of their nucleoplasm, are 

 identical as regards the ancestral germ-plasm which they con- 

 tain. During the whole process of segmentation and the entire 

 development of the embryo, the total number of ancestral 

 germ-plasms which were at first contained in the germ-plasm 

 of the fertilized egg-cell must still be contained in each of the 

 succeeding cells. 



Thus no objection can be raised against the view that the 

 four loops of the first polar body contain the ovogenetic nucleo- 

 plasm, that is to say, an idioplasm which contains the total 

 number of ancestral germ-plasms, but at an advanced and 

 highly specialized ontogenetic stage. 



The formation of the second polar body may be rightly con- 

 sidered as a ' reducing division,' as a division leading to the 

 expulsion of half the number of the different ancestral germ- 

 plasms, in the form of two nuclear loops, for no reason can be 

 alleged in support of the assumption that the four loops of the 

 second nuclear spindle are made up of identical pairs. Further- 

 more the facts of heredity require the assumption that the 

 greatest possible number of ancestral germ-plasms is accu- 

 mulated in the germ-plasm of each germ-cell, and thus that 

 the small number of loops not only means an increase in 

 quantity but a multiplication in the number of different an- 

 cestral germ-plasms present in each of them. If this conclusion 

 be correct, there can be no doubt that the second division of the 

 egg-nucleus means a reduction in the above-mentioned sense. 



But there are yet other observations which, if correct, must 

 also be considered as ' reducing divisions.' I refer to all those 

 cases in which the longitudinal splitting of the loops is either 

 entirely wanting, or does not occur until after the loops have 



' Wilhelm Roux, ' Beitrage zur Entwicklungsmechanik des Embryo,' 

 No. 3, Breslauer arztliche Zeitschrift, 1885, p. 45. 



