EXPERIMENTAL STUDIES ON THE DEVELOPMENT 

 OF THE EYE IN AMPHIBIA. 



II. ON THE CORNEA. 



WARREN HARMON LEWIS. 



• Associate Professor of Anatomy, Johns Hopkins University. 



With 2 Plates. 

 INTRODUCTION. 



With the introduction of the binocular dissecting microscope 

 the possibiHties ot investigating the subject of correlative embry- 

 ology have been greatly enhanced. With its aid, as I have already 

 pointed out in my paper on the origin of the lens in Rana palus- 

 tris, one can make with very delicate instruments exceedingly 

 minute dissections of the living amphibian embryo, and by trans- 

 plantation and extirpation of organs and tissues can gain an 

 insight into the influences of intra-organic environment in develop- 

 ment. Spemann's experiments on Rana fusca and my own on 

 Rana palustris establish without doubt the correlative character 

 of the origin of the lens in these two species and my unpublished 

 work on Rana sylvatica and Amblystoma punctatum show that 

 in these species likewise the lens is dependent for its origin on the 

 influence exerted by the optic vesicle on the overlying ectoderm. 

 .The cornea is likewise a correlative product, but of a quite dif- 

 ferent nature from the lens as will appear in the following pages. 

 While the lens is apparently dependent upon specific influences 

 from the optic cup, the cornea or rather corneal changes of the 

 ectoderm may be brought about by such different structures as 

 the lens alone or of the optic cup alone. Spemann^ concludes 

 that the clearing of the corneal ectoderm is dependent in Rana 

 fusca on the presence beneath the skin of the eye with its lens. 

 In my own experiments on Rana palustris- it was noted that in 



' Verhand. d. Anat. Gesel., 1901. 



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



