LEE BARKER WALTON 143 



underlying explanatory principles involved, which must 

 not be overlooked in a consideration of the changes which 

 may take place in hereditary units. These are concerned 

 with the differences involved in metabolism.^ 



On the one hand there are studies dealing with the direct 

 effects of a changed metabolism on the developing indi- 

 vidual. Here may be mentioned the work of Lillie in 

 connection with the "free-martin" of cattle; Steinach on 

 the transplantation of the gonads in rats and guinea-pigs; 

 Goodale on the grafting of ovaries in male fowls; Pearl 

 and Surface on the degeneration of the ovary in cattle; 

 Riddle with pigeons, etc. On the other hand, there are 

 studies dealing with the indirect effects on inheritance. 

 Among these may be mentioned that of Goldschmidt with 

 moths; Woltereck with daphnids; Plough with tempera- 

 ture effects on Drosopbila; Hoge with the effects of cold 

 on Drosopbila; Morgan with the effects of moist food 

 supply on Drosopbila, 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 cattle, 

 etc., resulted from the modifying influences of the sex 

 hormones in the male where the two chorions had anas- 

 tomosed. 



As an example of the inheritance group, Morgan has 

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

 pbila 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 Drosopbila the gene for the ab- 

 normality — or the chemical preparedness for the inhibi- 

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



^The theory has had a long historical development. Treat (1873) published a 

 paper on controlling sex in butterflies as a result of food supply. Yung (1881) 

 worked with tadpoles. Nussbaum (1897) with rotifers. Recent evidence of an 

 elaborate nature has been presented by Goldschmidt, Woltereck, Whitney, Banta, 

 Shull and others. 



