508 Experimental Studies on the Origin of the Lens in Amphibia 



cavity. The detached optic vesicle was transplanted by pushing it cau- 

 dally beneath the skin into the mesenchyme from the incision ah. Fig. 1 

 and allowed to develop there. The optic stalk is not formed at this 

 stage, as will be seen in Fig. 2. The optic vesicle and its cavity are 

 more or less conical in shape with the base attached to the brain. The 

 skin flap after the removal of the optic vesicle is turned back to its 

 original position and held there by the pressure of small pieces of silver 

 wire for a few minutes. Healing is rapid and a few hours are generally 

 sufficienj; to close the wound along the line of incision ab, Fig. 1. 



Experiment DF^^. 



The embryo, experimented upon as de- 

 scribed above, was killed two days after 

 the operation. The sections show a well- 

 formed optic cup on the left side with a 

 lens about 70/a in diameter. This lens is 

 entirely separate from the ectoderm, see 

 Fig. 3. On the right side is a small regen- 

 erated eye separated superficially from the 

 ectoderm by a single layer of mesenchymal 

 cells. The ectoderm is continuous over the 

 region of this regenerated eye and shows no 

 traces of changes leading to lens-formation. 

 If the conditions had remained normal a 

 lens of the diameter of the normal one 

 would have been present, or as we shall see 

 later if the regenerated eye were in contact with the skin changes leading 

 to lens-formation such as are found in experiments DF55 and DFjg 

 would probably be present. The transplanted portion of this eye lies 

 caudo-dorsally to the regenerated eye and is quite superficial. It is 

 about as large as the normal eye on the left side, has evaginated 

 but shows no signs of lens-formation. I think it very probable that the 

 regenerated eye would soon have stimulated lens-formation as in experi- 

 ments DF„, DF„ and DF,«. 



Fig. 3. 



^AptJiiHit; 



verse section throug-h the middle of 

 the reg'enerated eye. X 45 diameters 

 rg, regenerated eye. Ir, cephalic end 

 of transplanted eye. 



Experiments DF^^, DF^^, and DF^^. 



The embryos of these three experiments were killed as in DF54 two 

 days after the operation. In DF53 and DF55 the regenerated optic 

 vesicle is in contact with the ectoderm at which point the inner layer 

 of the skin is thickened showing the first beginnings of lens-formation, 



