124 AMPHIMIXIS OR ESSENTIAL MEANING OF [XII. 



miss the question ; we do know however that it is an actual fact. 

 We know that the paternal no less than the maternal nuclear 

 rods of the fertilized ovum possess the developmental tendencies 

 of the species, and that either of them alone, that is in the 

 absence of the other, are present in sufficient numbers to 

 regulate the development of the ^g%^ each set containing all 

 that is necessary to originate a mature individual of the species. 

 And the same fact holds good for each successive stage of 

 embryogeny, with just this difference, that the potentiality of 

 stages to come, and not of those passed through, is contained in 

 the embryonic cells. Furthermore every cell contains the 

 separate paternal and maternal nuclear rods, and either set is 

 capable of producing all the subsequent stages. This remains 

 true throughout the whole course of development, from the 

 fertilized ovum which produces the parent, to the male and 

 female germ-cells of the offspring. No real fusion of the two 

 nuclear substances into a single mass ever takes place, so that 

 the corresponding predispositions of the two parents are ar- 

 ranged together, but the hereditary substance contributed by the 

 father remains separate from that contributed by the mother. 

 These substances are made up of units of which each contains 

 those collective predispositions which are indispensable for the 

 building up of an individual, but each possesses an individual 

 character, i. e. they are not entirely alike. I have called such 

 units ancestral plasms, and I conceive that they are con- 

 tained, in larger or smaller number, in the chromatin of the 

 mature germ-cells of living organisms, viz. that the parental 

 nuclear rods are made up of a certain number of these. 



I have thus briefly called to mind the manner in which I 

 conceive that many such ancestral plasms are collected together 

 in a single nuclear mass, and the consequent necessity for a 

 ' reducing division.' It is not perhaps superfluous to return to 

 this subject once more. Each of the parental germ-plasms which, 

 at the phyletic origin of sexual reproduction, for the first time 

 fused together in the segmentation nucleus of the offspring 

 must have contained the potentiality of one individual only, 

 and must have been, in a certain sense, completely homogeneous. 

 Naturally, such a statement by no means excludes the existence 

 of a very complicated structure, in which a number of different 

 predispositions, or of different parts, are collected together, but 



