No. 518] SHORTER ARTICLES AND DISCUSSION 121 



investigated the enzymes in the skin of black, chocolate, yellow, 

 and albino mice, and reported finding enzymes for black, choco- 

 late, and yellow. Riddle criticizes Miss Durham's conclusions 

 for no other apparent reason than that they apparently oppose 

 his views. In albinos Miss Durham was not able to decide 

 definitely concerning the presence of enzymes but was of the 

 opinion that the enzymes were not present. Riddle's suggestion 

 that yellow is a blend between albino and black would be quite 

 interesting if we did not know that it is not true. Castle has 

 recently shown that the tendency to produce yellow pigment, 

 in rabbits at least, is a separately heritable tendency. On the 

 other hand, we can agree with Riddle's statement that the 

 ' ' data warrant the definite statement that yellow mice are forms 

 with the power of oxidizing tyrosin compounds, to an inter- 

 mediate point." 



If it were not for the well-established facts of segregation in 

 the inheritance of color, Riddle's statement that "in gametic 

 unions we deal not at all with factor particles but merely mix 

 and amalgamate to various degrees powers of tyrosin oxidation 

 and conditions supplied by the differentiations of tissues and 

 organs, together with environmental conditions external and 

 internal, supply whatever else is concerned in color produc- 

 tion." It is really to be regretted that Riddle does not know 

 more of the facts of color inheritance, for his incisive remarks 

 indicate that if he knew these facts and took proper cognizance 

 of them he would be highly useful to Mendelianists by way of 

 developing an explanation of Mendelian phenomena more in 

 keeping with the facts of physiological chemistry. 



His criticism of Castle's work on rabbits is entirely unfounded. 

 He assumes that the factors found by Castle can not exist apart 

 from pangenes of the de Vriesian type, each of which is wholly 

 responsible for the development of a Mendelian character. 

 Castle's work shows that he has no such idea. He merely worked 

 out the facts of color inheritance in rabbits, and, except for a 

 brief reference in his closing paragraph about a possible mechan- 

 ism for their explanation, gives no indication that he has any 

 theory to explain them. He certainly does not commit himself 

 to the de Vriesian theory. Castle has shown us that there are 

 three kinds of pigments in the hairs of rabbits whether they 

 should be there or not, and that the tendency, under norma; 

 conditions, to produce these pigments is hereditary ; furthermore. 



