Studies on Chromosomes . 23 



these stages a variable number of deeply-staining nucleoli make 

 their appearance; but their true nature can only be determined 

 positively when the whole ovarian life of the egg has been followed 

 and the process of maturation observed. I can, therefore, only 

 state that no chromosome-nucleolus is present in the contraction 

 period of synapsis, or in the early growth-period; and even though 

 it be present in later stages, which I think is very doubtful, a wide 

 difference between the sexes would still exist in respect to the 

 earlier period. 



F. General Resume 



The foregoing results may be given a general formulation as 

 follows : If n be the unreduced number of chromosomes in the 

 female, the matured eggs in all cases contain half this number ("). 

 The males are of three types. In the first, one of the chromo- 

 somes (the heterotropic or "accessory") is without a mate, and 

 the unreduced number is accordingly one less than that of the 

 female. Half the spermatozoa possess, and half lack, the hetero- 

 tropic chromosome, the first class having the same number as the 

 matured eggs ("), the second class one less (5-1). In the second 

 type the male has the same number of chromosomes as the female, 

 but possesses one large and one small idiochromosome while the 

 female possesses two large ones. In maturation half the spermat- 

 ozoa receive the small and half the large idiochromosome. The 

 third type differs from the second in that the idiochromosomes are 

 of equal size in both sexes, and no visible differences exist between 

 the two classes of spermatozoa or the somatic groups of the two 

 sexes. Designating the large and small idiochromosomes as 7 

 and / respectively, the relations in fertilization and sex-production 

 are as follows: 



TYPE I 



(PROTENOR, ANASA, ALYDUS, HARMOSTES) 



Egg " + spermatozoon ^ (including heterotropic) = n (female). 

 Egg 5 + spermatozoon i (heterotropic lacking) = n I (male). 



TYPE II 



(LYGAEUS, EUSCHISTUS, COENUS, PODISUS) 



Egg 5 (including /) + spermatozoon ^ (including 7) = n (including //) (female). 

 Egg ^ (including 7) + spermatozoon (including ') = n (including /') (male). 



