Wilbur L. Le Cron 249 
eration. It is evident that the impulse before removal of the optic vesicle 
was not sufficient to bring about any visible signs of self-differentiation. 
In another embryo (Experiment VIII,,) operated upon at this stage 
and killed three days afterwards, there is found on the left side a normal 
lens about 130, in diameter which has separated from the ectoderm, 
and on the right side a lens-plate—like thickening. At the time of the op- 
eration a very slight thickening of the ectoderm .in the right lens region 
was noted. In this experiment no regeneration of the eye took place. 
There has evidently, then, been great retardation or almost complete 
stoppage in the growth and differentiation of this lens-plate, owing, I 
believe, to the absence of the continued influence of the optic vesicle. 
Another embryo (Experiment VIII,,) of this stage operated upon 
and killed four days later has on the left side a lens-bud about 100 m in 
diameter. The latter is still attached to the ectoderm. The right eye 
is wanting, but there is a thickening of the ectoderm in the normal po- 
sition. The differentiation and growth of the right lens-plate has been 
much retarded, or perhaps has come to a standstill, evidently again 
through the loss of the influence of the optic vesicle. 
Another embryo (Experiment VIII,,), killed five days after only par- 
tial extirpation of the optic vesicle, shows on the left side the normal 
lens 130 » in diameter, just about ready to separate from the ectoderm. 
The regenerated right eye is deeply seated and separated from the ecto- 
derm by mesenchyme. The ectoderm over the eye is thickened into a 
lens-plate, but is much checked in development. Evidently the deeply 
situated, regenerated eye has exerted no influence upon the lens-plate. 
At the time of the operation a slight thickening of the ectoderm was to 
be seen. 
Another embryo (Experiment VIII,,) of this stage (VIII), from 
which the right eye was entirely removed, was allowed to live six days. 
At the time of the operation there was to be seen on the right side a 
slight thickening of the ectoderm for the lens-plate. The normal lens 
on the left side, about 150 in thickness, has separated from the ecto- 
cerm and shows considerable differentiation of its lens-fibers (Fig. 6). 
In the normal position on the right side there is a vesicular body sep- 
arate from, but close to, the ectoderm (Fig. 7). It consists of a single 
layer of high columnar epithelial cells surrounding a central cavity, and 
is about 110 in diameter. The appearance and general arrangement 
of the cells indicate very clearly that it is a lens-vesicle considerably re- 
tarded in development. It is also abnormal in that the medial pole 
shows only slight indication of the beginning of lens-fibers. Such elon- 
gation of the cells of the medial pole is always found, even before the 
nermal lens separates from the ectoderm. 
