158 Referate. 



In this series the pink eye was assumed to be the result of all that is 

 left when V is lost, and not the result of the activity of the factor P. On 

 the other hand, the letter was on a different basis from the letters P and Y. 

 It stood for a color and not for a factor that had been lost from the germcells 

 of the wild fly. In representing thus by a color which of course is really 

 formed by the action of other residual factors besides 0, considerable con- 

 fusion occurred when the factor was lost and an eosin eye appeared. Further- 

 more the case was still more complicated when progressive mutations arose. 

 Morgan's suggestion to overcome the difficulty follows. An abbre- 

 viation of the name of the character, as heretofore, stands as its symbol; 

 thus P stands for the pink factor and small p for its allelomorph. The large 

 letter represents merely the dominant character. The eye color series for 

 Drosophila then becomes: 



Red PYE 



Vermilion . . . . P v E 



Pink p Y E 



Vermilion -pink . . . p v E 



Eosin P Y e 



Eosin-vermilion . . P v e 



Eosin pink . . . . p Y e 



Eosin-pink-vermilion . p v e 



Castle agrees with Morgan that simplification of Mendelian formulae 

 is needed, but he says that Morgan's suggestion to allow the absence of 

 a factor to stand for a character, i.e. the factor P being present only 

 in animals that are not pink eyed, "is confusion worse confounded". 

 Further Castle states that investigators using the presence and absence 

 notation have made the system ridiculous. They start out, he says, as if 

 small a stands for nothing, then they make it stand for something. They 

 couple a und b. He asks, "How can nothing be inseparably bound up 

 with nothing"? All of which shows that Castle uses his factors as realities 

 and not as a notation. Castle's suggestion is to abandon the dual ter- 

 minology. A small letter is used to designate a variation which is reces- 

 sive in crosses with the normal, and a capital letter for a variation that 

 is dominant in crosses with the normal. 



This would give the following formulae for the Drosophila eye colors. 



Red normal 



Vermilion .... v 



Pink p 



Pink-vermilion . . p v 



Eosin e 



Vermilion-eosin . . p e 



Pink-eosin .... p e 



Pink-vermilion- eosin v p e 



Applying the same scheme to mice, the wild type and the seven muta- 

 tions in hair color that have occurred would be designated as follows: 



1. Wild =. gray 



