On Mendelian Dominance. 169 



hours it changes through gray and brown to black. PHISILAX was 

 able to observe the same changes in liquid pressed from the young 

 larvae. He concluded that the cause of change in color is due to 

 the action of the tyrosinase upon the tyrosin, these two substances 

 existing in the embryo long before development and it is probable 

 that they coexist in the egg or that they are deposited at the time 

 of ovogenesis*. Recently GoRTNER 1 } has shown in other cases that 

 the pigmentation of the insect larvae is due to the interaction of a 

 chromogen and a member of the tyrosinase group. RIDDLE 2 ) says 

 In accounting for melanin color characters I would maintain that 

 we can account for all the major happenings of color development 

 and inheritance with extremely little assumption. It is known that 

 one oxidase is concerned. It is known that the germ possesses 

 actively the power to oxidize amino acids. I think we need make 

 use of nothing in the germ but just this power. It is known that 

 the protoplasm of different species, of different tissues, of different 

 parts of the cell, possess different powers of oxidizing protein bodies. 

 The fate of color characters is then bound up 1) in the union of 

 these particular powers of the two germ cells; 2) in the origin 

 (through other outside developmental processes) of favorable and 

 unfavorable regions for tyrosin oxidations; and 3) in environmental 

 conditions. BATESON 3 ) states that In at least a large number of 

 cases the inheritance of characters consists in the transmission of 

 the power to produce something with properties resembling those 

 of ferments*. 



Such facts make reasonable the assumption that something of 

 the nature of an enzyme exists in the germ cell and is vitally con- 

 cerned in the development of inherited characters. While such 

 definite chemical compounds never have been isolated from the germ 

 cells, the assumption of the existence of such substances does much 

 to unify the many sided results in inheritance experiments as well 

 as to make clear some of the problems of the future. For the sake 

 of convenience, then, let us call these substances enzymes. Since 

 we know precisely many of the laws governing chemical reactions 

 in vitro, our theory enables us to explain, if not to predict, the re- 

 sults of chemical reactions concerned in fertilization and development. 



1) GORTNER, R. A., Journ. of Biol. Chera. (1910.) Vol. 7. p. 365. (1911.) 

 Vol. 10. p. 89. 



2) KIDDLE, 0., Biol. Bulletin. (1908.) Vol. 16. p. 339. 



3 ) BATESON, W., MENDEL'S Principles of Heredity. (1909.) p. 268. 



