THE CHROMOSOMES IN HEREDITY. 249 



My observations in regard to the accessory chromosome lend 

 support to the hypothesis of McClung l that of the four sperma- 

 tozoa arising from a single primary spermatocyte, those two 

 which contain this element enter into the formation of male off- 

 spring, while the other two, which receive only ordinary chromo- 

 somes take part in the production of females. If this hypothesis 

 be true, then it is plain that in the character of sex the reduction 

 occurs in the first maturation mitosis, since it is this division 

 which separates cells capable of producing only males from those 

 capable of producing only females. Thus we are confronted 

 with the probability that reduction in the field of one character 

 occurs in one of the maturation divisions and that of all the re- 

 maining characters in the other division. The significance of 

 such an arrangement, though not easy of perception, is neverthe- 

 less great. As regards their chromosome groups, the two cells 

 resulting from each 'reduction mitosis are conjugates and, there- 

 fore, opposites from the standpoint of any individual character. 

 Thus if we consider a hypothetical form having eight chromo- 

 somes comprising the paternal series A, B, C, D and the maternal 

 series a, b, c, d, one of the cells resulting from the reduction divi- 

 sion might contain the series A, b, c, D, in which case its sister- 

 cell would receive the conjugate series a, B, C, d. It is plain 

 that these conjugates, differing from each other in every possible 

 character, represent the most widely different sperms the organ- 

 ism can produce. Now if reduction in the sex-determining 

 chromatin also took place in this division it is apparent that these 

 two diametrically opposite series would enter into individuals of 

 different sexes ; but if the sex-reduction is previously accom- 

 plished by the asymmetrical distribution of the accessory in the 

 first division, then both the members of each conjugate pair must 

 take part in the production either of males or of females and thus 



forms most closely resemble the accessory, is also described by Montgomery (1901) 

 as dividing in the reducing division, and failing to divide in the equation division a 

 lact which is the more remarkable because in Protenor, as in all Hemiptera-Heter- 

 optera thus far described, reduction is accomplished in the first maturation division. 

 'McClung, C. E., "The Accessory Chromosome Sex Determinant?" Bioi.. 

 BULL., III., I and 2, 1902. "Notes on the Accessory Chromosome," Anat. Anz., 

 XX., pp. 220-226. 



