406 Wandering Cells and Muscles from the Optic Cup Epithelium 
fessor Nussbaum for his kindness and the exceptional privileges extended 
to me at the Anatomical Laboratory of the University of Bonn. 
Careful study of the ciliary region by means of complete serial sec- 
tions of chicks from two and one-half days to the period of striation 
of the muscle at about twelve days failed to furnish any evidence of an 
epithelial origin for the ciliary muscle. I studied with great care the 
outer layer of the optic cup in the iris and ciliary regions and even lat- 
eral to the ciliary region and also with especial care the cleft region. 
Professor Nussbaum drew my attention to a peculiar condensation of 
the mesenchyme (CH, Fig. 1) along the cleft, which I found to appear 
during the fourth day and to disappear during the eighth day. It had 
no connection with the origin of the ciliary muscle, but may possibly 
serve to strengthen the optic cup at what might be considered its weak 
s z 
ae NG OATS “8: 
ae OE 
Se 
Fic. 1. Tangential section through the optic cup of a chick 6 days, 13 hours old. 
Magnified 130 diam. Cl., cleft; C. H., cleft heap; E. B.; epithelial bud; W., nerve 
fibers; P., pupillary margin; P. Z., pigment layer; &. Z., retinal layer. 
place along the cleft. The cilary muscle appears to develop in silu 
from mesenchyme. Herzog came to the same conclusion. Between the 
optic cup and the place in which the ciliary muscle develops there is 
a considerable area of very loose mesenchyme (see Fig. 2), and it would 
seem easy to detect any migration of epithelial cells across it into the 
ciliary region if such a migration occurred. While working over this 
question my attention was attracted by certain peculiar buddings of the 
outer or pigment layer of the optic cup. More careful study has con- 
vinced me that many if not all of the pigmented cells lying amongst the 
connective tissue cells of the iris and the region lateral to the iris are of 
epithelal origin, arising from the outer layer of the optic cup. 
MATERIAL. 
Chicks of various ages (see table, p. 411) were hardened in Flemming’s 
solution and the anterior part of the eye cut into serial sections and 
stained in safranine. Others were hardened in Zenker’s fluid and 
