1830. ANNIVERSAKY MEMOIRS OF THE BOSTON SOCIETY OP NATUKAL HISTORY. 1880. 



THE DEVELOPMENT 



or A 



DOUBLE-HEADED VERTEBRATE. 



Bt SAMUEL F. QLAEKE, Ph.D., 



ASSISTANT IN BIOLOGY, JOHNS HOPKINS UNIVERSITY, BALTIMORE, MD. 



BOSTON: 



PUBLISHED BY THE SOCIETY. 



1880. 



