Xo. 5S3] BOLE OF ENVIRONMENT IN DROSOPHILA 423 



seen in the first two figures, is the more usual form of 

 abnormality in this stock; but modifications of other 

 rings shown in the other figures are probably due to the 

 same cause or causes. Two consecutive rings may form 

 a spiral as shown in c or half of a ring may be absent 

 as in e, or an entire ring may be lacking as in /. Indi- 

 viduals with abnormalities like those shown in the figures 

 were bred to each other usually three or four together. 

 Their progeny was examined and the normal and the ab- 

 normal types recorded. The latter were again used to 

 breed from for three or four generations. As no increase 

 in the proportion of abnormal offspring appeared, the 

 breeding was abandoned. The results given below are 

 in the order in which they were obtained without regard 

 to the generation in which they appeared. 



