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 V. 

 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 tlie 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 P V E 



Vermilion . . . . P v E 



Pink p y E 



Vermilion ]jink . . . p v E 



Eosin P V e 



Eosin-vermilion . . P v e 



Eosin pink . . . . p V 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 

 coujjle 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. Castles 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 c 



Pink-eosin .... p e 



Pink-vermilion eosin v p e 

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

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



1. Wild = g^ay 



2. a = albino 

 :i b = black 



4. c ^ cinnamon 



0. (1 = dilute 



G. p ^ pink- eyed 



7. s =: spotted 



8. y = yellow 



