250 Origin and Differentiation of the Lens 
Practically the same conditions are to be found in an embryo (Experi- 
ment VIII,,) killed nine days after the operation. There is no sign 
of a right eye, the normal left lens is about 160» in diameter, and is 
farther advanced than the one above. On the right side in the normal 
position for the lens there is a spherical body about 100 » in diameter. 
It consists of a single layer of high columnar cells surrounding a cavity. 
‘It is entirely separate¢ from the ectoderm, but lies near to it. The 
medial pole shows no indication of the formation of lens-fibers beyond a 
slight elongation of the cells. At the time of the operation a thickening 
of the ectoderm was noted. 
In another embryo (Experiment VIII,,), killed 30 days after the 
operation, there is complete absence of the right eye. Beneath the ecto- 
derm of the lens region on this side is a very degenerated-looking lens, 
about 110 » in thickness (Fig. 8). It consists of a layer of flat epithelial 
cells surrounding a spherical mass of irregularly arranged, degenerating 
lens-fibers. ‘The mass is much vacuolated, but stains rather like the 
lens-fiber part of the normal lens. The latter is 260m in diameter 
(Fig. 9). This experiment affords a marked instance of incomplete de- 
velopment and differentiation on the part of the lens when the influence 
of the optic vesicle is removed. 
From another embryo (Experiment VIII,,) of this stage, the optic 
vesicle was partially removed, and 10 days after the operation a well de- 
veloped eye had regenerated. The right lens has normally grown and 
differentiated, being almost as fully developed as the lens on the left 
side. Such instances where regeneration has occurred show that the 
operation itself of turning the ectodermal flap forward, does not inter- 
fere with lens development, provided the flap, when returned to its 
original position, comes into contact with a regenerated optic vesicle. 
Hence, whatever retardation of the lens may occur, must be explained by 
reasons other than by the immediate results of the operation. 
A series of 11 experiments was made upon embryos of a stage (1X) 
somewhat older than the above. A thickening of the inner layer of the 
ectoderm was perceptible, and the invagination for the developing lens 
could be seen from the surface (Figs. 10-11). 
Two embryos (Experiments IX,, ,,), killed eight days after the opera- 
tion, show lenses on the left sides normally developed, being about 170 p 
in diameter. On the right sides are small spheroidal bodies consisting 
of one or two Jayers of columnar epithelium surrounding central cavi- 
ties. Figures 12 and 13 are from mesial sections of the abnormal and 
normal lenses of one of these eight-day embryos. The right abnormal 
lens shows that the lens-plate (as seen in Fig. 11) continued its devel- 
