PLATE 81 



B 





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m 



A. Tail of Colwnba guinea (19, Dest-mate of mutant 20), age 79 days; ahows QOrma] 



whitish tail-band in dark feathers. 



B. Tail of C. ywmeo, mutant (20), age 78 days; ahows a weakened whitish tail- 



band, misplaced, in center of normal black-band. 



C. Tail of C. guinea (10, sister to mutant), age 125 'lays. 



