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THE AMERICAN NATURALIST [Vol. XLVIII 



dry; and more when the food was alkaline than when it 

 was acid. No other environmental factors were discov- 

 ered which influenced the production of Beaded wings. 



Selection of more or less extreme Beaded flies very 

 quickly moves the average Beadedness of the offspring 

 in the direction of the selection, but this selection appar- 

 ently becomes further ineffective in a very few genera- 

 tions. 



Mutation is of very frequent occurrence in the Beaded 

 stock and the new mutants obtained have in most cases 

 shown themselves to be produced under the influence of 

 one normally Mendelizing gene. 



I acknowledge with pleasure the kindly interest and 

 suggestions made from time to time by Dr. A. H. Sturte- 

 vant and Mr. H. J. Muller. These have been of much 

 assistance to me. My thanks are also especially due to 

 Dr. T. H. Morgan whose advice and criticisms at critical 

 points have never failed to aid in clearing up the situation, 



Baur, E. 1912. Einfiihrung in die experimentale Vererbungslehre. 

 Bridges, C. B. 1913. Non-disjunction of the Sex Chromosomes of Dro- 



sophila. Jour. Exp. Zool., Vol. 15. 

 Hoge, M. A. 1914. The Influence of Temperature on the Development of 



a Mendelian Character. Jour. Exp. Zool. In press. 

 MacDowell, E. C. 1914. Multiple Factors in Mendelian Inheritance. 



Jour. Exp. Zool., Vol. 16. 

 Morgan, T. II. 1911a. The Origin of Nine Wing Mutations in Drosophila. 



Morgan, T. II. 1911b. A Dominant Sex-limited Character. Froc. Soc. 

 Exp. Biol, and Med., Vol. 9. 



Morgan, T. H. 1912a. The Masking of a Mendelian Kesult by the Influ- 

 ence of the Environment. Proc. Soc. Exp. Biol, and Med., Vol. 9. 



Morgan, T. H. 1912?>. The Explanation of a New Sex-ratio in Drosophila. 



