513 Experimental Studies on the Origin of the Lens in Amphibia 



lens in the normal place on the right or operated-on side. The skin 

 over this region shows no signs of lens formation. Mesenchyme has 

 partially taken the place of the eye but not entirely, and there is a 



depression upon this side of the 

 head (see Pig. 9). The trans- 

 planted optic vesicle lies in the 

 cephalic end of the Wolffian body, 

 deep beneath the skin. It has 

 continued enlarging, invaginating 

 and differentiating, but without 

 signs of a lens. 



In series DF and IV there 

 were ninety experiments. The 

 embryos were killed from two 

 to eleven days after the opera- 

 tions. In fifty-seven of the em- 

 the eye and lens-formation. In 

 several of these the regenerated 63-6 was more or less deeply situated 

 but the instances where the lens is still attached to the ectoderm by a 

 long narrow pedicle give a clue to the origin of the lenses in the other 

 experiments where the regenerated eye &nd lenses are not close to the 

 skin. In three of the experiments where the eyes were more or less 

 superficial, no traces of lens-formation are to be found. In seventeen 

 experiments the regenerated eyes were deeply situated without possi- 

 bility of direct contact with the ectoderm and in no instance was there 

 a trace of lens-formation. In thirteen experiments regeneration of the 

 eye failed and in each instance no traces of lens-formation were found. 

 That the operation of turning the skin flap forward and then replac- 

 ing after removal of the optic vesicle does not interfere with lens for- 

 mation is evident from the numerous instances in which the regenerated 

 eye has enlarged sufficiently to touch the skin and stimulate lens forma- 

 tion, see Figs. 4, 5, 8, 14, 21, 23 and 25. 



Fig. 9. Experiment IV3. Transverse sec- 

 tion tliroug-h the middle of the eye region. 

 X 30 diameters. 



bryos there was regeneration of 



Experiment XI-^. 



This experiment, performed in a quite different manner from those 

 above, suggests the view that the lens will not form without the contact 

 influence of the optic vesicle on the skin. The skin over and about the 

 optic vesicle of E. palustris of stage II (see Figs. 1 and 2) was com- 

 pletely torn away and the head one-half of a slightly older embryo of 

 E. sylvatica was grafted upon the denuded area by its cut end. Nine 



