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Warren H. Lewis 2 
sylvatica. The transplanted optic vesicle invaginates and the various 
layers of the retina form. Most of the embryos were killed from 3 to 6 
days after the operation. In one allowed to live 17 days the pigment 
layer has broken down and its deeply pigmented cells are migrating into 
the mesenchyme. The various layers of the retina appear to show begin- 
ning disintegration. ; 
Lenses are associated with several of these transplanted eyes but as 
none of them are attached to the ectoderm one is not absolutely sure of 
their origin, but I believe that here, too, the optic vesicle of rana palustris 
can stimulate lens-formation from the ectoderm of amblystoma. The 
normal lenses associated with the eye of the amblystoma embryos are 
present and uninfluenced by the formation of other lenses. 
In six experiments the optic vesicles of rana sylvatica embryos were 
transplanted into the otic region of slightly older embryos of rana palus- 
tris. Such transplanted eyes go on differentiating and invaginating. 
In one experiment the embryo was killed 17 days after the operation and 
the transplanted eye, though very irregular in form, owing to distortion 
of transplantation, shows perfect differentiation of the layers of the 
retina and the pigment layer, and the latter in marked contrast to those 
transplanted into amblystoma, forms a continuous layer and shows no 
tendency towards migration of its cells. In three of the experiments 
lenses are associated with the transplanted eyes, in one a lens-like bud is 
still attached to the ectoderm by a long pedicle showing that such trans- 
planted eyes have the power of stimulating lens-formation from ectoderm 
of another species. 
The study of the reactions in the cross transplantation of tissues of 
various kinds into species as nearly related as rana palustris and rana 
sylvatica or as widely separated as rana and amblystoma offers a wide 
and interesting field of investigation. 
