346 Tlw Uuitij of the Organism 



nal characters, were these cliaracters exclusively maternal, 

 in spite of the fact that in some of the embryos in the two- 

 cell stage the nucleus of one of the cells seemed to be purely 

 female. That the variations from pure femaleness toward 

 the hybrid condition of this part of the skeleton were due 

 to fragments of chromatin from the male nucleus having 

 passed into the female nucleus, he regards as probable, for 

 he could observe that in the reconstruction of the nuclei, 

 both male and female, from the chromosomes during fertili- 

 zation, the male chromatic granules did not always remain 

 together, but were scattered about more or less, sometimes 

 mingling quite intimately with tliose from the female nucleus. 

 This would seem to give opportunity for contamination, as 

 one might say, of the female nucleus with male chromatin 

 even in those cases where, after the nuclei were reconstructed, 

 nothing of such contamination could be observed. But 

 Herbst is quite conscious of the danger in this sort of ex- 

 planation, that namely, w^hich having found some observa- 

 tional ground on which to base an explanatory assumption, 

 proceeds to push that assumption to whatever lengths may 

 be necessary in order to explain the facts as it is desired 

 they should be explained. 



The weight of this piece of evidence in favor of chromatin 

 as one "hereditary substance" is undoubtedly great, and is 

 enhanced not a little by the conservatism of the investigator 

 w^io presents it. How far it goes toward proving that chro- 

 matin is the hereditary substance is quite another matter, 

 and one to be dealt with later. 



The Connection of Sex with a Particular Chromosome 



The proof recentl}^ brought out that in some organisms 

 sex is connected with a particular chromosome in the germ- 

 cells is another point scored for the chromatin theory of 

 heredity. The first phase in this discovery consisted in 



