Warren H. Lewis 261 
distorted also. It is among these injured and distorted eyes, but more 
especially among the smaller transplanted eyes, that retardation in the 
differentiation of the retinal layers is to be observed during the early 
stages. When such eyes are transplanted into the same or even into the 
other species of rana they continue this progressive development for at 
least 20 days, which is as long as they were allowed to live. How much 
longer differentiation and growth would continue can only be determined 
by experiment. I have already shown that such transplanted eyes have 
the power of stimulating lens-formation from the strange ectoderm of the 
region into which they are transplanted.’ When in the proper relation 
with the ectoderm corneal changes will also take place in the ectoderm 
of the strange region. The anterior endothelial layer over the pupil of 
the eye will also form.’ All of these changes may take place except that 
of lens and corneal formation no matter what the orientation of the eye 
in the mesenchyme may be. 
Such transplanted eyes as a rule have no connection or contact even 
with the central nervous system of the host, each eye being as a rule 
entirely surrounded by mesenchyme or at least becomes so a few days 
after transplantation. Such eyes as are in contact or become connected 
with the central nervous system or other structures of the host are ap- 
parently unmodified by such connection except by the fusion of the 
transplanted and the normal eye or the transplanted and regenerating 
eye. 
If a portion of the transplanted eye projects into the ccelom a modifi- 
cation in the development of the pigment layer occurs in that the pigment 
layer fails to develop over this part of the eye. Fig. 7, from such an eye 
projecting directly into the ecelom, shows the pigment layer wanting 
here. Had the mesothelial lining of the ccelom been intact the pigment 
layer would probably have developed over this portion of the eye as it 
has over the transplanted eye seen in Fig. 8. Here the pigment layer is 
in contact with the mesothelial layer which prevents the eye from pro- 
jecting into the ccelom. 
It often happened that the cut separating the optic vesicle from the 
brain was in such a plane as to include a small amount of brain tissue, 
the latter remaining attached to one side of the optic vesicle. The re- 
sulting differentiation of the two tissues, after transplantation, into eye 
and brain tissue, may go on without the formation of an optic stalk, the 
4Lewis, Am. Jour. of Anat., Vol. VII, 1907, p. 145; ibid., Vol. III, 1904, p. 505. 
5 Lewis, Am. Jour. of Anat., Vol. VII, 1907, p. 161, Figs. 39, 41, and 42. 
