Carnegie Institution of Washington, Publication No. 205 



Paper No, 23 of the Station foe Experimental Evoltttion 

 AT CoiB Spring Habbor, New York 



From the Laboratory of Genetics, op the Btjssey 

 Institution, Forest Hill, Massachusetts 



Copies of this Book 

 wera first issued 



DEC 311914 



PRESS OF GIBSON BROTHERS, INC. 

 WASHINGTON, D. C. 



