Wilbur L. Le Cron 201 
opment for a short time after the operation to the formation of a lens- 
bud, and to its separation from the ectoderm as a lens-vesicle. Here its 
development was ultimately checked and no lens-fibers were formed. 
This lens-vesicle is much smaller than the normal lens, and its lack of 
differentiation is also very evident. 
This abnormal lens-vesicle is about the same size as a normal lens 
which has just separated from the ectoderm (see Fig. 19). It does not, 
however, show nearly the amount of differentiation of such a lens, 
especially in the region of the median pole, which shows no formation of 
lens-fibers, as does the normal lens. The cells of the median pole of this 
abnormal lens are somewhat elongated, as compared with those of the 
lateral pole, but this difference already existed in the lens-plate at the 
time of the operation. It seems, then, that the development of the lens- 
plate has been more in the change of form than internal differentiation. 
In two experiments (IX,, 4,) in which the embryos were allowed to 
live 11 and 14 days, the lenses of the corresponding sides are approxi- 
mately of the same size, and about the same amount of difference is 
found between the right and left lenses of each embryo. The lenses on 
the left measure about 190 » (compare Fig. 39), while those on the 
right are much smaller, being only about 100, in diameter. The latter 
(Fig. 14) are small spheroidal vesicles, consisting of a single layer of 
high columnar cells, and lying close to the ectoderm. In the cavity of 
the vesicle there are a few detached ectodermal cells, showing signs of 
degeneration. The cells of the epithelial wall of the vesicle are healthy in 
appearance, and more like those of the anterior epithelial layer of a 
younger normal vesicle (as in Fig. 19), than the more flattened cells of 
the left normal lens of the same embryo. The cells of the median pole 
of the abnormal vesicle, as in the preceding experiment, are somewhat 
elongated, as compared with those of the lateral pole. This lens-vesicle, 
although six days older than the one shown in Fig. 12, is much smaller. 
This diminution in size may have been caused by injury to the lens- 
plate, although at the time of the operation no injury was noted. On 
the other hand the lens-plate may not have been quite so far advanced 
at the time of the operation as the lens in the preceding experiment, and 
hence fewer cells of the inner layer of the ectoderm were influenced to 
take part in the formation of the lens-vesicle. Or, again, it may be after 
a certain time these abnormal Jens-vesicles decrease in size, perhaps by 
the migration of some of the cells into the vesicle. This point can only 
be settled by further experimentation. 
When the optic vesicle is removed after lens formation has begun, the 
development of the latter is not checked directly after, or by the im- 
itty 
