XIV Proceedings of the Association of American Anatomists 



In a second series of experiments performed as above, the optic cup 

 was transplanted to more caudal portions of the embryo. In one experi- 

 ment the eye remained superficial and a lens developed between it and 

 the skin. The deeply placed eyes failed to develop lenses, but they con- 

 tinued to grow, invagination and differentiation of the layers of the 

 retina taking place. 



In a third series, the skin was completely torn away from over the 

 optic vesicle and a piece of skin from the abdomen of Eana sylvatica 

 grafted onto this denuded area. In one of the experiments, the optic 

 vesicle succeeded in touching the skin and stimulating lens formation. 

 In the other experiments, the optic vesicles remained deep in the mesen- 

 chyme but continued to develop, invagination and differentiation of the 

 layers of the retina occurring, but the lens failed to form. 



In a fourth series of experiments, the head or tail of half of a 

 slightly older embryo of E. sylvatica was grafted by its cut surface onto 

 the denuded area over the side of the head of E. palustris. Tlie optic 

 vesicle was thus made to project toward the coelom or yolk of E. sylvatica. 

 In most of the experiments, the eye remained deeply buried ; in all such a 

 lens failed to develop, but in many, invagination went on and the layers 

 of the retina developed. In a few experiments, the position of the eye 

 altered and it touched the ectoderm, stimulating lens formation from 

 ectoderm near the junction of E. palustris and E. sylvatica. 



From these experiments, we may conclude: (1) The lens is abso- 

 lutely dependent for its origin on the influence of the optic vesicle on 

 the ectoderm. (2) There is no predetermined area of ectoderm which 

 must be stimulated in order that a lens may arise; the ectoderm is 

 probably equi-potential as regards its lens-forming power; more than 

 this even, the ectoderm of E. sylvatica is equi-potential with that of 

 E. palustris in this regard. (3) As after cutting away that part of the 

 optic vesicle which normally stimulates lens formation, the regenerated 

 eyes of various sizes will stimulate lens formation, it seems probable that 

 various portions of the optic vesicle have this power. (4) The lens is 

 not necessary for the invagination of the optic vesicle, nor are attachment 

 to the brain and the normal surroundings at the side of the head neces- 

 sary. 



Although an optic cup forms without the presence of a lens, the 

 chambers of the eye fail to develop and the lack of a vitreous humor is 

 especially noticeable and mesenchyme fills in the small irregular cavity. 

 The absence of a vitreous humor accounts for the small cup cavity, the un- 

 expanded eye and the thick layers of the retina. The same number of 

 layers develop but they are often twice as thick as normal. 



