538 Experimental Studies on the Origin of the Lens in Amphibia 



during the early stages of development such an origin would be very 

 uncommon in this species, Eana palustris. I shall show in a subsequent 

 paper that quite the contrary is the case in Eana sylvatica, as in this 

 species the optic cup readily gives rise to a lens from itself if prevented 

 from stimulating one from the ectoderm. 



CONCLUSIONS. 



These experiments lead to the conclusion that there is no especial 

 predetermined area of the skin which must be stimulated in order that 

 a lens may arise. 



They also lead to the conclusion that the lens is dependent for its 

 origin on the contact influence of the optic vesicle on the ectoderm, for 

 we find that when the optic vesicle touches the ectoderm not only under 

 normal conditions but under abnormal ones that* a lens arises at the 

 point of contact. 



The all-important influence of the optic vesicle is brought out most 

 forcibly by the demonstration of the power it possesses to cause the for- 

 mation of a lens from ectoderm taken from over the abdomen of a differ- 

 ent species. 



C. Are Various Portions of the Optic Vesicle Capable of 

 Stimulating Lens Formation? 



That various portions of the optic vesicle may stimulate lens forma- 

 tion is clearly indicated by some of the experiments already noted, as 

 where merely a corner of the optic vesicle reaching the skin is sufficient 

 to cause lens formation, see experiments IV9, Xlg,, XI30 and Xllg^. 

 This is more clearly shown by those experiments of series DF and IV 

 in which the regenerated optic vesicle formed a small but fairly normally 

 shaped eye with a normally shaped lens. See experiments DF55, Fig. 4 ; 

 DF,e, Fig. 5; IV„ Fig. 8; DF,„ Fig. 16; DF,„ Fig. 21; DF,3, Fig. 23; 

 DF,„ Fig. 25. 



Experiment IVo. 

 The operation was performed as on the other experiments of this 

 series. Three days after the operation the tadpole was killed. The 

 sections show that the head is considerably flattened on the right side 

 owing to the fact that the right optic vesicle is very small as compared 

 with the one on the left side. One corner of this small regenerated right 

 optic vesicle is in contact with the skin and here a lens is beginning to 

 differentiate from the ectoderm (see Fig. 37). On the left side there 

 is also a thickening of the ectoderm for the lens. The cells of the 



