

CD 



2? 





Caknegie Institution of Washington. Publication No. 179. 



Papi'.ks \ t os. 18 axd 19 of the Station for Experimental Evolution at Cold Spring 



Earbor, New York. 



Copies of this Bool* 

 were first issued 



SEP 131913 





n 



PRESS OF GIBSON BROTHERS 

 WASHINGTON, D. C. 



