^66 O.V THE NUMBER OF POLAR BODIES AND [VI. 



My opinion of the significance of the second polar body is 

 shortly this, — a reduction of the germ-plasm is brought about 

 by its formation, a reduction not only in quantity, but above all 

 in the complexity of its constitution. By means of the second 

 nuclear division the excessive accumulation of different kinds 

 of hereditary tendencies or germ-plasms is prevented, which 

 without it would be necessarily produced by fertilization. With 

 the nucleus of the second polar body as many different kinds 

 of idioplasm are removed from the egg as will be afterwards 

 introduced by the sperm-nucleus ; thus the second division of 

 the egg-nucleus serves to keep constant the number of different 

 kinds of idioplasm, of which the germ-plasm is composed during 

 the course of generations. 



In order to make this intelligible a short explanation is 

 necessary. 



From the splendid series of investigations on the process of 

 fertilization, commenced by Auerbach and Biitschli, and con- 

 tinued by Hertwig, Fol, Strasburger, van Beneden, and many 

 others, and from the theoretical considerations brought forvv-ard 

 by Pfliiger, Niigeli, and myself, at least one certain result fol- 

 lows, viz. that there is an hereditary substance, a material 

 bearer of hereditary tendencies, and that this substance is 

 contained in the nucleus of the germ-cell, and in that part of 

 it which forms the nuclear thread, which at certain periods 

 appears in the form of loops or rods. We may further main- 

 tain that fertilization consists in the fact that an equal number 

 of loops from either parent are placed side by side, and that 

 the segmentation nucleus is composed in this way. It is of no 

 importance, as far as this question is concerned, whether the 

 loops of the two parents coalesce sooner or later, or whether 

 they remain separate. The only essential conclusion demanded 

 by our hypothesis is that there should be complete or approxi- 

 mate equality between the quantities of hereditary substance 

 derived from either parent. If then the germ-cells of the off- 

 spring contain the united germ-plasms of both parents, it 

 follows that such cells can only contain half as much paternal 

 germ-plasm as was contained in the germ-cells of the father, 

 and half as much maternal germ-plasm as was contained in 

 the germ-cells of the mother. This principle is affirmed in 

 a well-known calculation made by breeders of animals, who 



