APPEARANCE OF THE SOMITES IN THE CHICK. 133 



opment of the embryo, namely, that differentiation begins at the 

 anterior end and progresses posteriorly. 



Hull Zoological Laboratory, 

 University of Chicago, 

 April 3, 1907. 



LITERATURE CITED. 

 Balfour, F. M. 



'85 Comparative Embryology. 

 His, W. 



'68 Untersuchungen liber die Erste Anlage des Wirbeltbierleibes. Leipzig. 

 Kupffer, C, and Benecke, B. 



'79 Photogramme zur Ontogenie der Vogel. Halle. 

 Mitrophanow, P. 



'97 Teratogenetiscbe Studiens, II. Archiv f. Entwickelungsmecbanik d. Organ- 

 isem, Bd. VI., Heft 1. 



Peebles, Florence. 



'98 Some Experiments on tbe Primitive Streak of the Chick. Archiv f. Entw.- 

 mech., Bd. VII., s. 405-429. 



Piatt, Julia B. 



'89 Studies on the Primitive Axial Segmentation of the Chick. Bull, of the Mus. 

 of Comp. Zool. Harvard Coll. Vol. XVIL, No. 4. 

 Von Baer. 



'28 Entwickelungsgeschichte der Thier. 



