Xa8 Arend. L. Hagedoorn and A. C. Hagedoorn. 



the germ from which the organism with tlie recessive character grew 

 up. Tlie fact, that this hypothesis was offered independently by 

 different authors, sufficiently shows how the facts called for it. 



By an analytical study of the germinal differences, which may 

 be seen in the most diverse groups of organisms, it was further found, 

 that only in those cases are we sure to find a "dominance" of one 

 character over another, in which two organisms crossed, differ in the 

 presence and absence of one single gene, and only, if this gene happens, 

 in the given instance, to influence the development in a visible way. 

 For it was soon observed, that, whereas there are sets of two and 

 more genetic factors, which do not interfere with each others action, 

 there are others which do. To give an example. The gene, which 

 by its presence or absence makes the difference between a black and 

 a chocolate mouse, is wholly independent, in its distribution, as well 

 as in its action, from that, which distinguishes normal mice from 

 waltzers. Thus, if we cross a black normal mouse to a chocolate 

 waltzer, we get black, normal young. Black is "dominant" over 

 chocolate and normal is "dominant" over waltzing. 



But if we mate a yellow-agouti mouse to a black one, we see 

 that black is not dominant to yellow-agouti, nor is it recessive to 

 yellow-agouti, for the young have a new colour, agouti. The yellow- 

 agouti had one gene which the black lacked, and reversely, and 

 these two genes, as genetic developmental factors, together with all 

 the others which yellow-agouti and black mice have both, make the 

 hybrids agouti. 



There is no question of dominance, which means, that dominance 

 is nothing fundamental, only a phenomenon shown in some cathe- 

 gories of crosses by certain characters over others. Now we might 

 still say, that "presence of black pigment is dominant over its 

 absence" and that "the agouti-distribution of colour over each hair' 

 is dominant over solid colour of the hair, but when we come to those 

 cases in which either one of two genes, which together have a marked 

 influence, or even both, have no influence when alone, we can not 

 do even this. We might even then speak of "latent characters" and 

 some authors still use this horrible conradictio in terminis, but we 

 think it better to reserve the term character for the actual qualities 

 of the organisms, and not to include in this term qualities which 

 they i/n^-Zif have had if the germ, or circumstances, had been different. 



Now we know that heredity is the transmission of a certain 

 cathegory of stuffs which we will call genes, and which in certain 



