304 



THE AMEBIC AN NATURALIST 



[Vol. LI 



eosin, of which the modifying factors give vis seven grades, is 

 itself only one of another series of seven grades that are due to 

 diverse alterations in the same unit factor — in the same chromo- 

 somal l(nMis. As we know from the studies of Drosophila, this 

 locus is a ccriaiii I't'jaidii of the X-chromosome. When this locus 

 retains its iioniial coiiditioii the eye is red. Some years ago a 

 variation was ohservt'd by which the eye lost its red color, be- 

 coming white. Somewliat later another variation came, by which 

 the eye color became eosin. By the wonderfully ingenious 

 methods which the advanced state of knowledge of the genetics 

 of Dro.wphila has made possible, it was determined that the 

 mutations white and eosin are due to changes in a particular 

 part of a particular chromosome, and that indeed the two are 

 due to different conditions of a particular region of the X-chro- 

 niosome. In other words, they show different conditions of the 

 same unit. INIoreover the normal red represents a third con- 

 dition of this same unit. 



Later a fourtli condition of this same unit was found, giving 



ni'w cdlof was cali.d clifrry. We liave now four grades of this 



And now. witli tli.- ininntc attention paid to the grades of eye 



of ani>lir.<. Ilyd." flintn adds two new -ra.h's. u,,,' rnWcd 

 ''blood." M..ar the rxttvni.' .v<l ,.nd of the series ; 1 he nWwv. ealled 



two from fed and white I'espect ively. So we have now six grades 

 of this nnit. And in the same nnniber of the same jonnuil. Safir 

 (1916. adds anotlier intermediate o,,,de. lyin- between tinged 



1. Red 



2. Blood 



3. Cherry 



4. Eosin 



