434 Warren Harmon Lnvis. 



corneal clearing ot the ectoderm were wanting in the skin cover- 

 ing the region from which the eye had been taken. I have 

 already given an experiment of this nature in my article on the ori- 

 gin of the lens in Rana palustris.^ In this embryo a skin-flap was 

 turned forward from over the optic vesicle, the latter cut away and 

 the flap returned to its original position without injury to the corneal 

 area of the ectoderm. The embryo was killed eleven days after 

 the operation but showed no signs of corneal changes on the side 

 operated on, while upon the normal side there was a well-developed 

 cornea. In other experiments similarly performed only a portion 

 of the optic vesicle was cut away and over the regenerated eye 

 corneal formation took place provided the regenerated eye was of 

 sufficient size to come into contact with the skin. It is evident 

 then that the lack of corneal formation after complete extirpation 

 of the eye was not due to the turning forward of the skin-flap. 

 If a skin-flap is turned forward from over the eye and then replaced 

 without injury to either it or the eye, perfectly normal develop- 

 ment of the eye, lens and cornea will ensue. A deeply situated 

 regenerated eye separated from the ectoderm by mesenchyme 

 will not cause corneal formation. 



In similar experiments on Rana sylvatica like results follow 

 total or partial extirpation of the eye. 



In Amblystoma punctatum the corneal changes are much 

 easier to follow than in Rana as the ordinary ectoderm is of con- 

 siderable thickness and the contrast betw^een it and the cornea 

 much greater than in the frog. 



In Amblystoma as in frog larvae the early total extirpation of 

 the optic vesicle, before the period of lens formation, results in 

 the failure of corneal development. For example, if in an embryo 

 at this stage a flap of skin is carefully turned forward from over 

 the eye, the optic vesicle completely cut away, and the uninjured 

 skin-flap returned to its original position, it readily heals in place 

 but no traces of corneal formation are to be observed even sixteen 

 days after the operation. Fig. i gives an accurate idea of the con- 

 ditions in such experiments. The lens also is entirely wanting 

 while on the normal unoperated side optic cup, lens and cornea 

 are present. The endothelial layer of the cornea likewise fails 

 to develop without the presence of the optic cup. 



1 Am. Jour, of Anat., vol. iii, p. 512, Fig. 9. 



