Il6 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII. 



than the first polar body ; the second must have some other 

 meaning, for if I had been correct in assuming the necessity of 

 the separation of the specific nucleoplasm from the egg, it 

 follows that this substance must be separated as fully and com- 

 pletely from the parthenogenetic as from the sexual egg. The 

 second polar body must therefore possess a different meaning. 

 In the fifth of the essays here collected \ I first indicated that 

 this meaning is a reduction in the substance which forms the 

 material basis of heredity, in that the number of the contained 

 ancestral plasms are diminished by one-half during the halving 

 of the nuclear substance to form the two daughter nuclei. By 

 the term ancestral plasms, I referred to the separate kinds 

 of germ-plasms from different ancestors which, according to 

 my view, must be contained in the germ-plasm of each indi- 

 vidual at the present day. If, before the introduction of sexual 

 reproduction, the germ-plasm of each living being contained 

 the developmental tendencies of one individual only, its structure 

 would be altered by sexual reproduction ; for after fertihzation 

 the different germ-plasms from two individuals would meet in 

 the nucleus of the egg ; furthermore, the number of these dif- 

 ferent kinds or units of germ-plasm must necessarily have been 

 doubled with each succeeding generation, so long, at least, as 

 they could have divided, preparatory to fertilization, without 

 relinquishing the power of giving rise, collectively, to the 

 whole organism, — that is, until the units had reached the mini- 

 mal limits of their mass. From this point onwards sexual re- 

 production could only have been rendered possible either by a 

 doubling of the nuclear substance, or since this was impossible, 

 by a halving of the germ-plasm of both germ-cells before each 

 act of fertilization, a halving which was not only quantitative, 

 but was above all a separation of the contained individual units, 

 a separation of ancestral germ-plasms, or briefly of ancestral 

 plasms. 



Hence, after the discovery of the law of the number of polar 

 bodies, I interpreted the first division of the nucleus as the re- 

 moval of ovogenetic idioplasm from the egg, and the second as 

 a halving of the number of ancestral units contained in the 

 germ-plasm. Such halving must have occurred, or the number 

 of ancestral units would have been doubled. It necessarily 

 ^ Vol. I. pp. 257-342. 



