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THE AMERICAN NATURALIST [Vol. XLIX 



In these counts there were normal to abnormal flies both 

 of whose parents were abnormal. Since the normals also 

 throw some abnormals it is probable that there is here a 

 case of multiple factors like that of beaded and truncate. 

 Special tests will therefore be necessary to work out the 

 case. 



The abnormal abdomens shown in Fig. 3, a-f, are from 

 another stock, discovered by Mr. Bridges. While some of 

 the types are not unlike those of the last series, they are 

 more extreme and there can be no doubt but that the two 

 stocks have a different composition. 



In the last drawing the entire fly is figured (the one 

 wing present has been cut off at the base), the upper half 

 of the thorax is absent. This same condition appears in 

 rather high proportions in certain other stocks, notably 

 in vestigial stocks. Even both sides of the thorax may 

 be absent so that the head rests above on the abdomen. 

 Although I have tried a number of times to obtain pure 

 stocks of this thoracic abnormality, I have never suc- 

 ceeded in getting a stock that did not throw a high per- 

 centage of normal individuals. 



This type of abnormal abdomen appeared in a cross 

 between a cream male and an eosin female as a single 

 female, Fig. 1, a, which had only three instead of five 

 bands in the abdomen. She was mated to one of her 

 brothers, and produced offspring all of which as far as 

 known had normal bands. A pair of these offspring gave 

 in the next generation abnormal bands in about half of 

 the flies. The abnormal band acted as a recessive. In 

 subsequent generations the character behaved in an irreg- 



