270 The Origin and Differentiation of the Optic Vesicle 
EFFECTS OF Cross TRANSPLANTATION ON THE GROWTH AND DIFFEREN- 
TIATION OF THE OPTIC VESICLE. 
Optic vesicles from rana sylvatica were transplanted into the region 
between the eye and ear of amblystoma embryos of various ages, namely, 
from a time before there are any traces of lens-formation until the lens- 
bud is well developed and nearly ready to pinch off. Fifty experiments 
were made and the embryos allowed to live from 2 to 27 days after the 
operation. The majority were killed 3, 4, and 5 days after transplan- 
tation. In most of these the transplanted optic vesicle goes on differen- 
tiating and growing in a very normal manner, invagination may take 
place and in 3 or + days the outer pigment layer is well differentiated. 
In the 5 days the invagination has progressed and not only the pigment 
laver but the other layers of the retina are clearly to be distinguished 
(Figs. 27 and 28), and in some of the embryos the optic nerves can be seen 
passing through the retina to the outer layer or into the mesenchyme. 
Not only is the optic vesicle under such conditions capable of self-differ- 
entiation and unaffected apparently by its environment, but it is prob- 
ably capable of stimulating lens-formation from the ectoderm of the 
amblystoma? This will be more fully considered in a later paper. In 
some of the embryos the anterior endothelial layer formed from the 
mesenchyme of the amblystoma (Fig. 28) extends over the pupil and 
lens. 
Unfortunately, all but 4+ of the embryos were killed during the 
first 6 or 7 days, but one, however, was killed 17 days, two 19 days, and 
one 27 days after the operation. In the ones killed 17 and 19 days after 
the operation the cells of the pigment layer have undergone a most 
curious change, they no longer form a continuous layer about the retina 
but are scattered in the mesenchyme about the eye as large heavily pig- 
mented cells. There are some indications of disintegration of the rest 
of the eye, yet, for the most part, the retina with its various layers is 
quite normal in appearance. 
In the embryo killed 27 days after the operation only a few scattered 
cells were to be found. Unfortunately, this is the only embryo allowed 
to live so long and more experiments will be necessary before a final 
statement can be made of the ultimate effect on the transplanted eye of 
the surrounding environment. One of my pupils is now at work upon 
this question. 
Twenty-five similar experiments were made of transplanting the optic 
vesicles of rana palustris embryos to the preotic region of amblystoma 
embryos of various stages. The results are identical with those of: rana 
