Wilbur L. Le Cron 255 
thus has the appearance of influencing lens-differentiation. However, 
these few experiments prove nothing, but suggest the questions, whether 
the nasal pit is capable of influencing lens development or not, and 
whether the lens-fiber pole may be formed at different parts of the lens 
circumference. 
In the following stage (XIII) (Fig. 29), the lens vesicle is quite well 
developed (Fig. 30), with a definite medial pole and the beginning of 
the formation of lens-fibers. It is completely divided off from the ecto- 
derm, but still in partial contact with the same. It is found that the 
normal lens, after complete division from the inner layer of the ecto- 
derm, still adheres or sticks to the same, and only after a certain time 
really separates from the ectoderm,—the processes of dividing off and 
separating not being simultaneous. Such a well advanced lens does not 
show at once any particular changes in development when the optic cup 
is removed. The lens-vesicle has evidently received something of a mo- 
mentum from the continued influence of the optic cup, and now, after 
removal of this influence, develops for a short time apparently inde- 
pendently. 
In an embryo (Experiment XIII,,) of this stage, killed four days 
after the operation, no particular difference between the two lenses is 
noticeable (Figs. 31-32). The medial poles are well defined and the 
lens-fibers within have a healthy appearance. The right Jens is still in 
contact with the overlying ectoderm, but otherwise appears like the 
normal left lens. Both measure about 140 in diameter, and are per- 
fectly developed. This experiment shows that the lenses of embryos of 
such a late stage (XIII) have power of considerable self-development 
after the removal of the optic cup. It requires some time before a 
marked difference in growth and in differentiation can be observed, but 
the difference invariably occurs, showing that the lack of influence of the 
optic cup is ultimately felt. 
In an embryo (Experiment XIII,,) killed seven days after the opera- 
tion, the left lens measures 170» and the right one 140 in diameter. 
The latter is thus somewhat smaller. It is well separated from the 
ectoderm, and contains normal lens-fibers. The medial pole, however, 
is rather obliterated by the epithelial covering of the lens (Fig. 33), and 
is not nearly so definite as in the normal lens (compare Fig. 13). 
In a still older embryo (Experiment XIII,,) which was killed nine 
days after the operation, a greater difference is to be seen. The left 
lens is about 200 » in diameter, while the right one measures only 150 p, 
and is considerably smaller than the former (Fig. 34, and compare 
Fig. 9). It lies rather close to the ectoderm, and contains some healthy 
