OTIC AND OPTIC PRIMORDIA IN MAN 203 
as a joint paper in the Carnegie Institution’s ‘Contributions 
to Embryology.” Although Dr. Evans’ own material, his ex- 
tensive studies on embryos in the European collections and in 
the Mall collection have been used freely, this part appears 
under my name as I am assuming complete responsibility for the 
interpretation of the nervous system. Needless to say, I am 
under great and varied obligations to Doctor Evans which I 
gladly acknowledge. The work was begun at the suggestion of 
the late Dr. F. P. Mall, to whom we owe much. Dr. G. L. 
Streeter has continued to support it and has helped and advised. 
Most of the drawings are the work of Mr. J. F. Didusch, whose 
understanding help has been invaluable. 
We would express our appreciation of the courtesy of Profs. 
Franz Keibel, A. C. F. Eternod, and H. D. Senior for permission 
to study the young human embryos in their collections. 
To the following physicians we are indebted for the embryos 
of our own series, for their cooperation and for the care which 
they took to preserve these delicate specimens: Dr. J. P. Spooner, 
of Peru, Indiana, for H279; Alpheus B. Streedain, of Chicago, 
for H87; Dr. Edwin Hirsch, of Chicago, for H637; Dr. Robert 
T. Legge, of Berkeley, California, for H 197; Dr. Ethel Rice, 
of Chicago, for H392; Dr. J. F. Burkholder, of Chicago, for H8. 
The exceptional success we have had in obtaining young embryos 
has been due in large measure to the support and cooperation of 
Dr. R. R. Bensley. 
THE OTIC PRIMORDIUM 
The earliest sensory primordium that can be recognized in 
man is a thickening of the ectoderm opposite the neural folds 
of the hindbrain. This is the beginning of the otic plate. Sev- 
eral statements in the literature indicate that the otic plate 
appears early in human development. In 1908 Keibel identified 
‘die Hérplatte’ in the Unger embryo (Normentafel 4), which 
had about nine somites. Wilson (14, p. 325) suggested that 
a pair of diffuse thickenings in his two- to three-somite embryo 
(H3) might be the ‘auditory areas.’ Tracing the otic plate back 
through our series leaves little doubt but that he was correct 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 34, NO. 2 
