No. 605] SHORTER ARTICLES AND DISCUSSION 307 



The Defect. — When viewed from the dorsal surface the defect 

 appeared as a blister of variable size on the proximal and 

 posterior part of the wing. From the ventral surface it appeared 

 as a pit. Occasionally a real blister filled with fluid was ob- 

 tained. The position of the defect was constant ; when small it 

 lay in the posterior cell just below the discal cell. When large 

 it involved nearly the whole wing including the axillary, anal, 

 second basal, discal and posterior cells. Usually both wings were 

 affected alike, but here and there flies were found with one 

 wing normal and the other wing severely affected. 



This factor is strikingly similar, both in its appearance and 

 the variability of its behavior, to the ' ' balloon wings ' ' found by 

 Morgan- in Drosophila and more recently fully described by 

 Marshall and Muller.^ The flies carrying the defect, in my cul- 

 tures, were very frequently sterile, and in no case did their 

 fertility begin to approach that of normal stock. 



In breeding, the character behaved as a mendelian recessive. 

 Normal crossed with balloon gave, in the generation, 196 

 normal and no affected individuals. (This included 4 matings.) 

 When brother and sister were mated, in the F2 generation, 312 

 normal and 111 balloon offspring were obtained This is very 

 close to the expected 3 : 1 ratio, of a monohybrid cross. When 

 balloon flies were crossed, all individuals were affected (74 off- 

 spring obtained) but the character showed itself extremely vari- 

 able; in some cases the flies appeared normal until very closely 

 examined. 



The defect was not sex-linked as is shown by the following 

 mating. A defective female was mated with a normal male of 

 normal stock. Of the 50 offspring resulting both males and 

 females were normal. 



The variation in the appearance of the balloon flies suggested 

 either that the size of the blister was dependent upon some 

 unknown environmental factors, or else, was due to multiple 

 allelomorphs or multiple factors. A great number of matings 

 were made to gain light on this point, but due to the sterility 

 of the affected individuals, the evidence is not sufficient to allow 

 us to draw any conclusions. Two individuals both of whom were 

 severely affected were crossed. The 20 offspring resulting were 

 all severely affected. Two individuals, both of whom were only 



2 In Morgan 's " A Critique of the Theory of Evolution. ' ' 



' Marshall and Muller, Jour, of Exp. ZooL, Vol. 22, 1917. 



