+-------------------++---------------------------------------+ | || Second generation. | | First |+----------+--------+-------------------+ | generation. || | | w^c v | +---------|---------+| | | ------- | | | || | | d_p | | Wild- |Depressed|| | +---------+---------+ | type | [male] ||Reference.| | | ~ |[female] | [male]. || |[female]|Cherry | ~ |[female].| || |[female]|vermilion|Depressed| | | || | | | | | | || | | [male]. | [male]. | +---------+---------++----------+--------+---------+---------+ | 21 | 31 || 19 I | 59 | 23 | 24 | +---------+---------++----------+--------+---------+---------+ +---------------------------------------------------------+ | Second generation. | +-------------------+-------------------------------------+ | w^c d_p | w^c | w^c d_p v | | --+----- | -----+-- | --+----+--- | | v | d_p v | | +---------+---------+--------+---------+---------+--------| ~ | | | | | | ~ Cherry | | Cherry |Depressed|Cherry | Wild- | |depressed|Vermilion| |vermilion|depressed| type | | | | | |vermilion| | | [male]. |[male]. |[male]. | [male]. | [male]. | [male].| +---------+---------+--------+---------+---------+--------+ | 6 | 6 | 5 | 5 | 0 | 0 | +---------+---------+--------+---------+---------+--------+ {68} CLUB. In May 1913 there were observed in a certain stock some flies which, although mature, did not unfold their wings (text-fig. H_a_). This condition was at first found only in males and suspicion was aroused that the character might be sex-linked. When these males were bred to wild females the club-shaped wings reappeared only in the F_2 males, but in smaller number than expected for a recessive sex-linked character. The result led to the further suspicion that not all those individuals that are genetically club show club somatically. These points are best illustrated and proven by the following history of the stock: [Illustration: FIG. H.--Club wing. _a_ shows the unexpanded wings of club flies; _c_ shows the absence of the two large bristles from the side of the thorax present in the normal condition of the wild, b.]