THE JOURNAL 
OF 
EXPERIMENTAL ZOOLOGY 
HDLTED BY 
WILLIAM E..CastLEe , Jacques LorB 
Harvard University The Rockefeller Institute 
Epwin G. CONKLIN Epmunp B. WiLson 
Princeton University Columbia University 
CHARLES B. DaveNPORT THomas H. Morean 
Carnegie Institution Columbia University 
HeRBERT S. JENNINGS Grorce H. Parker 
Johns Hopkins University Harvard University 
FRANK R. LILLIE RAYMOND PEARL 
University of Chicago Johns Hopkins University 
and 
Ross G. Harrison, Yale University 
Managing Editor 
VOLUME 31 
JULY—NOVEMBER, 1920 
THE WISTAR INSTITUTE OF ANATOMY AND BIOLOGY 
PHILADELPHIA, PA. 
