STUDIES ON CHROMOSOMES 



III. THE SEXUAL DIFFERENCES OF THE CHROMOSOME- 

 GROUPS IN HEMIPTERA, WITH SOME CONSIDERA- 

 TIONS ON THE DETERMINATION AND INHERI- 

 TANCE OF SEX 



BY 



EDMUND B. WILSON 

 WITH Six FIGURES 



Since the time of Henking's able paper on the spermatogenesis 

 of Pyrrochoris ('91), it has been known that in certain Hemiptera, 

 and in some other insects, a dimorphism exists in the nuclear con- 

 stitution of the spermatozoa, one-half of them containing the so- 

 called "accessory" or " heterotropic " chromosome, while in the 

 other half this chromosome is lacking. The meaning of this fact 

 has hitherto remained undetermined. McClung in 1902 devel- 

 oped an hypothesis of sex-production based on the conjecture that 

 the heterotropic chromosome is a sex-determinant, and more 

 specifically that spermatozoa containing this chromosome produce 

 males, for the very obvious, yet fallacious, reason that it is present 

 in the male. This hypothesis was based simply on the fact 

 that the spermatozoa are of two numerically equal classes, like 

 the sexes of the adults; and it was apparently overthrown by 

 subsequent observation. The hypothesis implied that the cells 

 of the female must contain one chromosome less than those of 

 the male; and although McClung did not specifically place his 

 assumption in this form, he considered it extremely improbable 

 that the accessory chromosome, or "any such- element," is present 

 in the egg. Sutton ('02) believed that he had found a 

 confirmation of this in the grasshopper Brachystola, where he 

 showed that the number in the male (spermatogonia) is twenty- 

 three, and stated that in the female (oogonia and follicle- 



JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. in, No. i. 



