THE THEORY OF SEX 609 



easily understandable, as well as the meaning of the j^eculiar 

 mechanism of mitosis. The formation of a chromosome means, 

 physically, the same thing as the dropping of a piece of charcoal 

 into a solution containing enzjanes. 



Harrison and Doncaster^ showed some time ago that species- 

 crosses of the moth Biston exhibit phenomena which will prob- 

 ably prove to be of the same type as intersexuality in the 

 gypsy-moth. In one of these crosses, also, exclusively males are 

 produced. (I may take the opportunity' to add here that some 

 years ago I, also, studied species-crosses of Biston and that my 

 results, as far as they went, agree with Harrison's experiments. 

 However I dropped the work because of the difficulties in breed- 

 ing, due to the systematic distance between the forms.) Har- 

 rison and Doncaster studied then the chromosomes of the two 

 parental forms and found that one of the species had very much 

 larger elements than the other. They suggested, therefore, that 

 size of chromosomes or quantity of chromatin might be the real 

 thing underlying our conception of different potencies. As a 

 matter of fact we had not overlooked this possibility, and my 

 assistant; J. Seiler, had studied the chromosomes of European 

 and Japanese gypsies. In his paper*^^ which was in press when 

 Harrison and Doncaster's was published he gives pictures of the 

 chromosome-sets of those forms and states that the Japanese 

 form has slightly larger chromosomes. The difference was, how- 

 ever, not great enough to appear very important. We have re- 

 cently investigated this point again and compared the chromo- 

 some sizes of many races of known potencies. The result is not 

 very encouraging, as nothing like a parallel between potency 

 and chromosome size could be found. In figure 53 is given a 

 photograph of the equatorial plate of the first maturation di- 

 vision in the spermatocytes of one of the forms with very high 

 potency of the sex-factors (the Japanese race A) ; figure 54 rep- 

 resents the same stage under the same magnification from the 



5 Harrison, 1. W. H. and Doncaster, L. On hybrids between moths of the 

 gr'ometrid subfamily Bistoninae, etc. Journ. Genetics, iii, 1914. 



^ Seiler, J. Das Verhalten der Geschlechtschromosomen boi Lojiidopteren. 

 Arch. f. Zcllforsch.. 13, 1914. 



