INHERITANCE 237 



VARIATION AND MUTATION 



Heredity, it has been said, may be understood as resting 

 upon the fact that each organism forms its own initial 

 stage again, and that this initial stage always encounters / 

 conditions of the same kind. 



If this statement were quite correct, all the individuals 

 of a given species would be absolutely alike everywhere 

 and for ever. But they are not alike ; and that they are 

 not alike everywhere and for ever is not merely the only 

 real foundation of the so-called theory of descent we 

 possess, but also forces us to change a little our definition 

 of heredity, which now proves to have been only a sort of 

 approximation to the truth, convenient for analytical 

 discussion. 



In the first place, the conditions which surround the 

 initial stages of morphogenesis are not quite equal in every 

 respect : and indeed the offspring of a given pair of parents, 

 or better, to exclude all complications resulting from 

 sexual reproduction, or amphimixis, as Weismann called 

 it the offspring of one given parthenogenetic female are 

 not all equal among themselves. The individuals of each 

 generation are well known to vary, and it is especially in 

 this country that the so-called individual or fluctuating 



and " Zellen-Studien VI." Jen. Zeitschr. 43, 1907) has made it highly probable 

 by experiments that the different chromosomes of the nucleus of the sexual 

 products play a different part in morphogenesis, though not in the sense of 

 different single representatives of different single organs. This doctrine, of 

 course, would not alter the whole problem very much : the chromosomes 

 would only be means of morphogenesis and nothing else, no matter whether 

 they were of equal or of different formative value. It only is with regard to 

 the problem of the determination of sex (see page 107, note 3), that the 

 morphogenetic singularity of one certain specific chromosome can be said to 

 be proved. 



