Warren Harmon Lewis 531 



40, drawn while the tadpole was in xylol, shows on the right side a re- 

 generated eye with a lens. The eye seems normal in shape and nearly 

 as large as the normal one on the left side. The sections show a nor- 

 mally developed eye except that the optic cup and lens are somewhat 

 smaller in size than the normal one on the left side. 



The optic vesicle in this experiment, as in experiment IV9, was cut 

 off so as to remove all of that portion which would normally have come 

 in contact with the skin and stimulated lens formation. The portion 

 that was left, however, has had the same power of stimulating lens for- 

 mation. 



Experiment II^q. 



This experiment was performed on the same sized embryo and at the 

 same time as experiment II^i. Thirteen days after the operation the 

 tadpole was killed. Fig. 41, an outline of the tadpole when in xylol, 

 shows the small regenerated right eye. Fig. 42, a section through 

 the center of both eyes, shows the small regenerated right eye with a 

 small lens. This eye and lens are apparently both normal except for 

 the smaller size. The right lens is about 130/x and the left lens about 

 ITOju, in diameter. In this experiment more of the optic vesicle was 

 probably cut away than in experiment IIn or it may have been slightly 

 more evaginated. In either case the amount of material left attached 

 to the brain destined to form the optic vesicle was probably less than in 

 experiment 11^. Yet here again a portion of the optic vesicle which 

 was never destined to stimulate lens formation did so. 

 t 



CONCLUSIONS. 



The experiments indicate that various parts of the optic vesicle may 

 stimulate lens formation, which means, I think, that at this early period 

 many or even all of the cells of the optic vesicle or perhaps even all of 

 those which are destined to take part in its formation have the power 

 of stimulating lens formation. 



GENERAL CONCLUSIONS. 



1. Neither a lens nor a trace of a lens will originate from the ecto- 

 derm which normally gives rise to one if the contact of the optic vesicle 

 with the skin is j^revented. 



2. There is no predetermined area of the ectoderm which must be 

 stimulated in order that a lens may arise. On the contrary various 

 portions of the skin when stimulated by the contact of the optic vesicle 

 may and do give rise to a lens. ISTot only will a lens arise from various 



