No. 508] 



NOTES AND LITERATURE 



245 



metabolic products as it has metabolic activities. Doubtless some 

 of these products will be similar for a number of chromosomes. 

 We may thus represent the chromosomes and their functions : 



(A A) — functions a, b, c, d, 



(BB) — " b, o, d, e. 



(CC) — " a, b, d. 



(EE) — " a, b, f. 

 Etc. Etc. 

 Now, of the numerous B chromosomes in the species, some may 

 perforin the function e in a manner differing from the others. 

 This function may fail entirely in some of them. Let us assume 

 that the production of horny substance requires that the functions 

 a, b, e and f shall be normal. If in a given group of individuals 

 the function e fails, which function may represent the produc- 

 tion of a given chemical substance in the cell, then horns fail to 

 develop. Individuals without horns would thus be represented 



(AA) — a, b, c, d. 

 (BB) — b, c, d. 

 (CC) —a, b, d. 

 (EE)— a, b, f. 

 Etc. Etc. 



Omitting from consideration those chromosomes which are not 

 concerned in the hereditary difference in question and remem- 

 bering that the poll character is dominant, the heterozygote 

 between the horned and polled forms would be 



B— b, c, d, e; B — b, c, d (heterozygote polled). 

 Generation F 2 would consist of 



1. B — b, c, d, e; B — b, c, d, e (horned). 



2. B b, c, d, e; B — b, c, d (heterozygote polled). 



3. B— b, c, d; B — b, c, d (homozygote polled). 



or three polled to one horned. Thus we derive the well-known 

 Mendelian ratio entirely independently of any idea of unit char- 

 acter in the germ plasm. Rather we assume that horns are due 

 to the presence in the cell of certain substances each produced 

 by the chromosomes, as a result of their chemical constitution: 

 and the poll character is due to the failure of a single chromo- 

 some to perform a particular function. When a hereditary 

 difference between two varieties is thus due to a difference in a 

 single set of homologous chromosomes, such difference will be- 



