520 Experimental Studies on the Origin of the Lens in Amphibia 



an the left side, is invaginated and shows differentiation of the layers 

 of the retina. It is deepty situated being on the mesial side of the otic 

 capsule, see Fig. 24. There is no sign of a lens in connection with it. 



Experiment DF^^. 



As in the experiment above the embryo was killed four days after 

 the operation. The condition of the regenerated eye is very similar to 

 that in experiment DF43. The medium sized regenerated eye is separ- 

 ated from the ectoderm by a considerable thickness of mesenchyme. A 

 small lens about 40/x in diameter lies in the optic cup. It is still con- 

 nected with the ectoderm by a long narrow epithelial pedicle which passes 

 through the layer of mesenchyme separating the optic cup and skin. 

 The sections of this embryo are cut obliquely to the stalk and in Fig, 25 

 the stalk is from a composite of two sections. The transplanted eye is 

 situated just in front of the otic capsule and between it and the skin is 

 a considerable thickness of mesenchyme, see Fig. 26. The transplanted 

 eye is about as large as the normal one on the left side. It shows invagi- 

 nation and differentiation of the layers of the retina. There is no trace 

 of a lens in its neighborhood. The diameter of the normal lens is about 

 140/^. 



The conditions found in the regenerated eyes in the above two experi- 

 ments can readily be explained on the supposition that the pressure of 

 the silver wire on the skin flap over the stump of the amputated eye 

 was sufficient to hold the ectoderm in contact with the regenerating eye 

 until the adhesion between them was accomplished. This adhesion which 

 is normally followed by the development of the lens had the same effect 

 in these experiments, but during the process of lens-development the 

 rapidly growing mesenchyme forced its way between the eye and skin 

 pushing the latter outward and separating it from the small eye and its 

 short optic stalk. A pull was thus exerted on the inner layer of the ecto- 

 derm owing to the adhesion between the lens and eye. 



Three other embryos killed four days after the operation have super- 

 ficially situated transplanted eyes with lenses. Eleven embryos killed 

 at the same time show deeply situated transplanted eyes without traces 

 of lens-formation or lenses in their neighborhood. 



Of three embryos, killed four and one-half days after the operation, 

 in two the regenerated eyes were deeply situated and without lenses. 

 The transplanted eyes in these two were superficial, one has a lens and 

 the other is without one. In the third experiment the regenerated eye 

 is superficial and has a lens while the transplanted eye is deeply placed 

 and is without a lens. 



