432 Warren Harmon Lewis. 



this species likewise corneal clearing of the ectoderm fails when 

 the eye is wanting. In this paper it will be clearly shown, how- 

 ever, that corneal clearing of the ectoderm in Amblystoma will 

 occur over a naked lens or over the optic cup without the lens, 

 provided the lens or cup are close to the overlying ectoderm. 

 If this be true for Amblystoma it probably holds also for other 

 amphibia and consequently Spemann's conclusion for Rana fusca 

 should be modified to this extent. 



In a preliminary communication before the Association of 

 American Anatomists, at Philadelphia, 1903,^ concerning my 

 experimental studies on the development of the eye in amphibia, 

 the following conclusions were given for the cornea: "(i) The 

 cornea fails to develop when the optic vesicle is entirely removed. 

 (2) Over the regenerated eye with lens a cornea develops, nor- 

 mally, except for size, which is small to correspond to the small 

 regenerated eye. (3) If the optic cup is torn out after the lens 

 has separated from the skin, a small area of clear epithelium will 

 develop immediately over the undisturbed lens. (4) Such clear- 

 ing for the cornea will also develop over an optic cup, from which 

 the lens has been extracted, but not in all cases." 



These conclusions were based mainly upon experiments on 

 Amblystoma punctatum and Rana palustris. More recent experi- 

 ments on Rana sylvatica show that in this species also the cornea 

 fails to develop when the eye is wanting. The present paper is 

 concerned more especially with the conditions in Amblystoma, 

 which is a more favorable form for the study of corneal forma- 

 tion than Rana. The experiments enable me to consider only 

 the early stages of corneal formation, namely: (i) The thinning 

 of the ectoderm of the corneal area; (2) the clearing of this 

 ectoderm and loss of its pigment; (3) the formation of the endo- 

 thelial layer of the cornea, which is in reality the anterior wall 

 of the anterior chamber of the eye. 



In addition to the above conclusions some of my more recent 

 experiments show that the cornea will form from ectoderm other 

 than that which normally gives rise to the cornea. 



This spring I have repeated most of the experiments on Ambly- 

 stoma and find that it is easy to confirm all of the conclusions 

 stated above. Some new experiments show that even after the 



1 Am. Jour, of Anat., vol. iii. 



