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THE AMEBIC AN NATURALIST [Vol. XLVIII 



value of F 1 counts, matings in pairs, and back-crosses to 

 normal. It stands however as the only evidence of its 

 sort that I can give at present. 



TABLE XVI 



Type 3 is not easy to explain. There are no known 

 cases of this sort elsewhere in Drosophila and I prefer 

 not to attempt to answer this question at present. 



In general, it may be noted that technical difficulties 

 have disturbed the crosses with second chromosome char- 

 acters. The wing character Arc is not always easy to 

 recognize, as it is very often nearly normal in appearance. 

 On the other hand, the flies with Curved wings, though 

 always distinct, occasionally get 4 'stuck up" with the 

 food and in their bedraggled condition it can not always 

 be determined whether or not the wings are Beaded as 

 well as Curved. I was at first inclined to attribute the 

 apparent coupling (which was discovered for Arc and for 

 Curved before it was discovered for Black) to errors 

 made in the counts. 



As for Black, the Fj and later generations give a much 

 lower percentage of Beaded offspring than do most other 

 crosses, and this necessitates raising large numbers of 

 offspring. The results are, however, trustworthy when 

 obtained. 



