154 THE AMERICAN NATURALIST [Vol. XLV 



where sex-determination can be diagnosticated cyto- 

 logically. 



In the discussion as to the existence of true graft- 

 hybrids the cytological configurations have of course a 

 high importance as precisely defined characters of cells 

 in such cases where the cytological elements of the two 

 species in question are different. And, as it may be well 

 known, cytological evidence is not at all favorable for the 

 idea of graft-hybrids. But the use of cytological configu- 

 rations for diagnosis is quite different from the idea that 

 special cytological elements might have importance for 

 the phenomena of heredity. 



The question of chromosomes as the presumed "bearers 

 of hereditary qualities" seems to be an idle one. I am 

 not able to see any reason for localizing "the factors of 

 heredity" (i. e., the genotypical constitution) in the 

 nuclei. The organism is in its totality penetrated and 

 stamped by its genotype-constitution. All living parts of 

 the individual are potentially equivalent as to genotype- 

 constitution. In botany there has been no doubt as to 

 this conception, and as to animals, 0. Hertwig has for a 

 long time advocated the same view against the views of 

 Weismann and others, who have suggested that ontogene- 

 sis is partly determined or at any rate accompanied by a 

 progressive simplification of the "anlagen" (as we say 

 the "genotype-constitution") in the cells of the growing- 

 embryo. The agencies of normally varying ambient con- 

 ditions and the interactions of specialized parts in the 

 developing individual may exercise their strong influence 

 upon the whole phenotypical state of the resulting partic- 

 ular individual. But these factors will as a rule not 

 change or shift the fundamental genotypical constitution 

 of the biotype in question. Later on we shall touch the 

 problem of such genotypical changes (the mutations) 

 induced by external factors. 



Here we have to point out the fact that "living 

 matter"— or, with a more precise definition, those sub- 

 stances or structures the reactions of which we call 



