Studies on Chromosomes. 543 



APPENDIX. 



During the summer, and since the foregoing paper was entirely 

 completed in its present form, I have obtained new material which 

 shows decisively that the theoretic expectation in regard to the 

 relations of the nuclei in the two sexes, stated at p. 539, is 

 realized in the facts. In Anasa, precisely in accordance with the 

 expectation, the oogonial divisions show with great clearness one 

 more chromosome than the spermatogonial, namely, twenty-two in- 

 stead of twenty-one; and the same number occurs in the divisions 

 of the ovarian follicle-cells. Again in accordance with the expec- 

 tation, the oogonial groups show four large chromosomes instead 

 of the three that are present in the spermatogonial groups. In 

 other respects the male and female groups are closely similar. In 

 like manner, the oogonial divisions in Alydus and Protenor show 

 fourteen chromosomes, the spermatogonial but thirteen; and in 

 Protenor the spermatogonial chromosome-groups have but one 

 large chromosome (unquestionably the heterotropic) while the 

 oogonial groups have two such chromosomes of equal size. 



The interpretation is unmistakable. Taking Protenor as a 

 type, all of the matured eggs must contain seven chromosomes, 

 of which one, much larger than the others, corresponds to the 

 heterotropic chromosome present in one-half of the spermatozoa. 

 These spermatozoa (seven-chromosome forms) contain a chromo- 

 some-group exactly similar to that of the egg; and fertilization by 

 a spermatozoon of this class produces a female having fourteen 

 chromosomes. The other half of the spermatozoa (six-chromo- 

 some forms) lack the heterotropic chromosome; and fertilization 

 of an egg by a spermatozoon of this class produces a male having 

 but thirteen chromosomes, the unpaired one being derived from 

 the egg and appearing in the maturation of this male as the 

 heterotropic chromosome since it is without a mate. There can, 

 therefore, be no doubt that a definite connection exists between 

 the chromosomes and the sexual characters, and I believe that 

 the conclusion can hardly be escaped that the chromosome- 

 combination, established at the time of fertilization, is, in these 

 insects, the determining cause of sex. 



The result reached in Anasa is confirmed by a comparison of 

 the male and female chromosome-groups in Lygaeus, Ccenus and 

 Euschistus, all of which possess in the male a pair of unequal 



