540 Edmimd B. Wilson. 



it is represented by a corresponding larger one (both sexes having 

 the same number of chromosomes). Were the small chromo- 

 some to disappear, the female would show one more chromosome 

 than the male in accordance with my general assumption. 



We have now therefore good reason to hope that observation 

 will directly determine whether sex is predetermined in the chro- 

 mosome-group; and further, whether the sex-determining func- 

 tion can be localized in a particular chromosome or pair of 

 chromosomes, as McClung suggested. 



5. The foregoing offers no specific suggestion as to the mean- 

 ing of the four classes of spermatozoa observed in Banasa. But it 

 may be remarked that the existence of two or four (or more) 

 classes of germ-cells in the same sex is in itself nothing anomalous; 

 for as Sutton has pointed out, under the conception of himself 

 and Montgomery there may be as many classes of spermatozoa 

 as there are combinations of paternal and maternal chromo- 

 somes (in accordance with the Mendelian ratios). Forms which 

 possess idiochromosomes or heterotropic chromosomes differ 

 from the more usual ones only in that two or four of these classes 

 are made visible by a greater or less differentiation of the members 

 of one or two of the chromosome-pairs. It seems admissible to 

 suppose that such a visible differentiation of the members of 

 particular chromosome-pairs may stand for a corresponding 

 differentiation of corresponding or allelomorphic qualities in the 

 adult. I would therefore suggest the possibility that such a 

 visible polymorphism of the male germ-nuclei as exists in Banasa 

 may be accompanied by a visible polymorphism in the adults; 

 and, while I am not aware that such a polymorphism has been 

 observed in the Hemiptera, I believe this subject should be care- 

 fully examined. 



It is hardly necessary to point out, finally, how strong a support 

 the foregoing observations lend to the general hypothesis of the 

 individuality of chromosomes, and to the conception of synapsis 

 and reduction first brought forward by Montgomery and developed 

 in so fruitful a way by Sutton and Boveri. I must frankly confess 

 that until I had followed step by step the behavior of the idiochro- 

 mosomes and the m-chromosomes in the Hemiptera I did not appre- 

 ciate how cogent is the argument brought forward in Montgomery's 

 paper of '01 in support of his conclusion that synapsis involves an 

 actual conjugation of chromosomes two by two, and that the 



