440 Warren Harmon L 



ewis. 



does the skin become as thin as that of the normal cornea. The 

 pigment disappears and the large vacuolated cells which are 

 present in the surrounding ectoderm are absent. (See Fig. 8, 

 Experiment MG4.) 



If, however, the lens is disturbed by the operation so that 

 mesenchyme grows in between it and the skin, the corneal changes 

 do not occur. (See Fig. 9, from Experiment Maj, and Fig. 3, 

 from Experiment MEj.) 



If after the optic cup is taken out the lens is transplanted a 

 short distance from the normal position, the mesenchyme often 

 separates the lens from ectoderm and in such experiments the 

 corneal clearing likewise fails to develop, and a condition similar 

 to that seen in Fig. 9 is present. 



F. Corneal Formation from Strange Ectoderm. 



If the ectoderm covering the optic cup and lens is completely 

 torn away at a stage shortly after the separation of the lens from 

 the ectoderm but before there are any visible corneal changes, 

 the wound thus formed will heal by the ingrowth of ectoderm 

 from the sides of the denuded area. In many of the experiments 

 there was more or less disintegration of the optic cup before the 

 wound healed. In some almost the entire optic vesicle disappears; 

 in others but little of it is lost. In the experiments where the 

 optic vesicle remains of sufficient size to come into contact with 

 the new ectoderm true corneal formation follows, the size of 

 the cornea varying with the size of the eye. In Experiment 

 XV362 (Fig. 10), there was very little loss of optic vesicle substance 

 and the new ectoderm soon covered the entire denuded area. 

 The cornea with its endothelial membrane is apparently normal 

 except in size being of less extent than the normal in proportion 

 as the eye is smaller than normal. The new cornea was not 

 well developed until about four days after the normal one on the 

 left side had become perfectly clear. The difference in time in 

 the formation of the corneas on the normal and operated sides 

 may be even much greater than this, as when there is considerable 

 disintegration of the eye, after the skin is torn off from over it, 

 healing may be delayed a day or so and the eye much reduced in 

 size. In some of these experiments the corneal clearing may be 

 delayed from four to eight days after the one on the normal side is 



