40 



tion of the ordinary chromosomes is 

 effected, the accessory divides longi- 

 tudinally.-^ 



My observations in regard to the 

 accessory chromosome lend support to 

 the hypothesis of McClung ^^ that of 

 the four spermatozoa arising from a 

 single primary spermatocyte, those 

 two which contain this element enter 

 into the formation of male offspring, 

 while the other two, which receive 

 only ordinary chromosomes take part 

 in the production of females. If this 

 hypothesis be true, then it is plain 

 that in the character of sex the reduc- 

 tion occurs in the first maturation mi- 

 tosis, since it is this division which 

 separates cells capable of producing 

 only males from those capable of pro- 

 ducing only females. Thus we are con- 

 fronted with the probability that 

 reduction in the field of one character 

 occurs in one of the maturation divi- 

 sions and that of all the remaining 

 characters in the other division. The 

 significance of such an arrangement, 

 though not easy of perception, is 

 nevertheless great. As regards their 

 chromosome groups, the two cells re- 

 sulting from each reduction mitosis are 

 conjugates and, therefore, opposites 

 from the standpoint of any individual 

 character. Thus if we consider a hypo- 

 thetical 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 



25 The chromosome .r of Frotenor, which 

 of all chromosomes in non-orthopteran forms 

 most closely resembles the accessory, is also 

 described by Alontgomery (1901) as dividing 

 in the reducing division, and failing to divide 

 in the equation division — a fact which is the 

 more remarkable because in Frotenor, as in 

 all Hemiptera-Heteroptera thus far de- 

 scribed, reduction is accomplished in the 

 first maturation division. 



2^ McClung, C. E., "The Accessory Chro- 

 mosome — Sex Determinant?" Biol. Bull., III., 

 1 and 2, 1902. "Notes on the Accessory Chro- 

 mosome," Anat. Anz., XX., pp. 220-226. 



SUTTON 



the reduction division 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 

 organism can produce. Now if reduc- 

 tion in the sex-determining chromatin 

 also took place in this division it is 

 apparent that these two diametrically 

 opposite series would enter into in- 

 dividuals of different sexes; but if the 

 sex-reduction is previously accom- 

 plished by the asymmetrical distribu- 

 tion of the accessory in the first divi- 

 sion, then both the members of each 

 conjugate pair must take part in the 

 production either of males or of 

 females and thus all extremes of chro- 

 mosome combination are provided for 

 within the limits of each sex. 



POSTSCRIPT 



The interesting and important com- 

 munication of Guyer ^^ on "Hybrid- 

 ism and the Germ-Cell" is received too 

 late for consideration in the body of 

 this paper. This investigator also has 

 applied conclusions from cytological 

 data to the explanation of certain phe- 

 nomena of hereditv% and his compara- 

 tive observations on the spermato- 

 genesis of fertile and infertile hybrids 

 are an important contribution to the 

 cytological study of the subject. The 

 conclusions drawn are of great inter- 

 est but, I think, in some cases, open to 

 criticism. In assuming that there is a 

 "segregation of maternal and paternal 

 chromosomes into separate cells, which 

 may be considered 'pure' germ-cells 

 containing qualities of only one 

 species" (p. 19), he repeats the error 

 of Cannon which has alreadv" been 



2" Guyer, M. F., "Hybridism and the 

 Germ-Cell," Bulletin of the University of 

 Cincinnati, No. 21, 1902. 



