522 Experimental Studies on the Origin of the Lens in Amphibia 



Experiment DF^^. 



The embryo was killed seven days after the operation. There is no 

 trace of a regenerated eye or lens in its neighborhood. The large and 

 very irregular transplanted eye lies ventral to the otic capsule. The eye 

 must have been injured gratly in transplanting and although differen- 

 tiation of the retina has gone on the various layers are very much mixed 

 up. This eye is very deeply situated and has two large and well-formed 

 lenses, each at about the same stage of differentiation as the normal one 

 on the left side. The two lenses are some distance apart, one projecting 

 from the cephalic surface of the eye and lying ventro-mesially to the otic 

 capsule, it measures about 140|U, in diameter; the other projects caudally 

 and lies dorsal to the anterior end of the Wolffian body, it is about 100|U, 

 in diameter. The normal lens on the left side is about 180/a in diameter. 

 Neither of these lenses could have come from the overlying ectoderm, 

 they must have originated either from the optic cup itself or from epi- 

 thelial cells carried from the edge of the wound into the present situation 

 with the transplanting of the eye. That the extensive injury to the 

 optic vesicle may have stimulated it in some way to give rise to the lenses 

 is not improbable. 



In three other embryos, killed seven days after the operation, the trans- 

 planted eyes are deeply buried and without lenses. 



Two embryos, killed eight days after the operation, have deeply situated 

 transplanted eyes without lenses. 



Of two embryos, killed eleven days after the operation, one lacks en- 

 tirely a regenerated eye and lens and the transplanted eye is deeply situ- 

 ated and without a lens. The other shows a regenerated eye with a lens 

 and a superficially transplanted eye without a lens. 



There are seventy-one experiments of the series DF and IV in which 

 the embryos show transplanted eyes. The embryos as we have already 

 noted were killed from two to eleven days after the operation. Thirty- 

 eight embryos show superficially situated transplanted eyes, that touch 

 or nearly touch the ectoderm, some of them are separated from the ecto- 

 derm by a thin layer of mesenchyme. Twenty-five of these have lenses 

 (one QjQ has two lenses), nine of the lenses are still attached to the 

 ectoderm; seventeen of the lenses are separate, but lie in such a position 

 as to indicate that they might have come from the ectoderm. In thirteen 

 embryos the more or less superficially situated transplanted eyes touch 

 or nearly touch the ectoderm and are without lenses. Why the optic 

 vesicles should not have stimulated lens-formation in these experiments 

 cannot be determined at present. In thirty embryos the transplanted 



