Warren Harmon Lewis 415 
pigment layer, which diminishes in thickness and pushes tongue-like 
into the cleft between the bud and the inner layer until it reaches the 
angle indicated by A, Fig. 15. In many of the specimens this tongue 
of the pigment layer does not seem to fuse with either the bud or the 
inner layer; in other specimens it is impossible to determine whether 
fusion has taken place. It is thus unlikely after the first separation of 
the bud from the outer layer that it receives any more cells from it. It 
remains attached to the inner layer, which may contribute to the enlarge- 
ment of the bud, but it seems more likely that the lengthening of the 
bud is brought about by extension 
of the pupillary margin of the optic 
cup towards the centre of the pupil 
Fie. 14. Fie. 15. 
Fie. 14. Diagram of the position of the sphincter buds arising from the pigment 
layer of the iris in a chick 13 days old. Mag. 25 dia. Sph.’ and Sph.’’ correspond to 
same in figures 11 and 12. 
Fig. 15. Radial section of margin of optic cup of chick 6 days, 22 hours old. Mag. 
550 dia. A., angle between sphincter bud and inner layer. 
by multiplication of cells in both the inner layer and the bud. The 
tendency to narrowing of the pupil is more than counteracted by the 
general expansion of the optic cup. 
CONCLUSIONS. 
Most, if not all, of the wandering pigmented cells in the stroma about 
the anterior portion of the optic cup during the first 14 days, and prob- 
ably later, arise from buds of the pigment or outer layer of the optic cup 
and are thus ectodermal in origin. 
The M. sphincter pupillae anlage is formed not only by buds from the 
pupillary margin, but its peripheral portion is formed by many distinct 
buds arising from the pigment layer some distance lateral to the pupil- 
lary margin of the optic cup. 
