CARNEGIE INSTITUTION OF WASHINGTON, PUBLICATION No. 23. 



PAPERS OF STATION FOR EXPERIMENTAL EVOLUTION AT 

 COLD SPRING HARBOR, NEW YORK. No. 2. 



CONTRIBUTIONS FROM ZOOLOGICAL LABORATORY OF MUSEUM OF COMPARA- 

 TIVE ZOOLOGY AT HARVARD COLLEGE. E. L. MARK, DIRECTOR. No. 158. 



PRESS OF GIBSON BROS., 

 WASHINGTON, D. C. 



