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THE AMERICAN NATURALIST [Vol. LII 



tance. Among these may be mentioned that of Gold- 

 schmidt with moths; Woltereck with daphnids; Plough 

 with temperature effects on Drosophila; Hoge with the 

 effects of cold on Drosophila ; Morgan with the effects of 

 moist food supply on Drosophila, etc, 



As an example of the development group, the investi- 

 gation of Lillie may be noted. The evidence obtained 

 showed that the "free-martin" or sterile female usually 

 developing where the twins are of separate sexes in cat- 

 tle, etc., resulted from the modifying influences of the sex 

 hormones in the male where the two chorions had anas- 



As an example of the inheritance group, Morgan has 

 found that the "mutant" "abnormal abdomen" in Droso- 

 phila occurs in connection with a moist food supply. The 

 character is a sex-linked dominant. If an abnormal male 

 is bred to a normal female and the food is kept moist, the 

 sons are normal and the daughters abnormal. If the food 

 is dry both sons and daughters are normal. The recipro- 

 cal cross gives sons and daughters both abnormal with 

 moist food but normal with dry food. 



It follows then that in Drosophila the gene for the ab- 

 normahty-or the chemical preparedness for the inhibi- 

 tion of normality, if one so wishes to term it-is per- 

 formed in the "X" chromosome and merely awaits a 

 suitable environment before presenting itself as a char- 

 acter. Similarly, in connection with the changes occur- 

 ring m the development of the "free-martin" of cattle, 

 it seems necessary to admit that there are genes present 

 m the sex chromosome concerned with the development 

 of sexual characters which, however, are in a state of 

 equilibrium, and that the inhibition or the excitation 5 of 

 one or the other genes or groups of genes will result in 

 the development of the corresponding individual. 



From the facts presented, one seems justified in making 

 the deduction that heredity hands down a framework 



