2 Edmund B. Wilson 



cells) the number is twenty-two, supporting this statement by a 

 single figure (op. cit., Fig. n). Sutton was, however, able to 

 examine only a very few of the female groups, and the object is 

 an unfavorable one as compared with the Hemiptera, owing to 

 the less compact form of the chromosomes. McClung's hypothe- 

 sis seemed to be rendered completely untenable by the later obser- 

 vations of Montgomery on Anasa ('04), and of Gross on Syromas- 

 tes ('04), both these authors describing and clearly figuring the 

 same number of chromosomes (twenty-two) in the male and the 

 female cells. Gross and Wallace ('05) were thus independently 

 led to the conclusion that only one of the two classes of spermat- 

 ozoa was functional, namely, that in which the heterotropic 

 chromosome is present. Those of the other class were assumed 

 to degenerate after the fashion of polar bodies. 



I am now able to bring forward decisive proof that the appar- 

 ently adverse evidence brought forward by Montgomery and 

 Gross was based on errors of observation, and that the sexes in 

 Hemiptera of this type do in fact show a constant difference in 

 the number of chromosomes. As far as these animals are con- 

 cerned, however, McClung's conjecture as to the mode of fertili- 

 zation proves to have been the reverse of the truth; for it is the 

 female, not the male, that possesses the additional chromosome, 

 as I have determined beyond all doubt in four genera, namely, 

 Anasa, Alydus, Harmostes and Protenor. The facts leave no 

 doubt that both forms of spermatozoa are functional; that all of 

 the eggs possess the same number of chromosomes; that all con- 

 tain the homologue, or maternal mate, of the accessory or hetero- 

 tropic chromosome of the male; and that fertilization by sper- 

 matozoa that possess this chromosome produces females, while 

 males are produced upon fertilization by spermatozoa that do 

 not possess it. 



A second type of dimorphism of the nuclei of the spermatozoa 

 was made known in the first of these studies. In this type all 

 of the spermatozoa contain the same number of chromosomes, but 

 half of them contain a large "idiochromosome" and the other 

 half a corresponding small one. I was led in that paper to suggest 

 the possibility that the idiochromosomes might play a definite 



