56 THE PINEAL ORGAN 



shows a transverse section through the larva fourteen days after the 

 operation. In other cases negative results were obtained or a small lens- 



L. 



r:" j \ 









c? s V 



..'.■-Si. ^'■.• : v--V>^:? i ' ' :;E ■ ■ V :' ;, --v ...-. '■••.■' 









/ 



/ 



Fig. 41. — Self-differentiation of the Lens. 



Transverse section through larva of Rana esculenta, fourteen days after extirpation 

 of the presumptive eye-rudiment. A lens L. has developed, although no 

 optic cup was present. 



(From Huxley and de Beer, after Spemann.) 



like thickening of the epidermis occurred in the situation in which the 

 lens should have been developed if the optic cup had been present. 



Fig. 42. — Lens formed from the Margin of the Optic Cup. 



The presumptive eye-rudiment of an embryo of Triton was grafted into the side of 

 the body of another embryo. The optic cup, not being in relation with 

 epidermis, has formed a lens from its own margin. 



Br. : portion of grafted brain tissue. L. : lens. 



Int. : wall of intestine. Ep. : epidermis of ventral wall. 



(From Huxley and de Beer, after Adelmann, Arch. Entzumech., 113, 1928.) 



3. Lens formation from the edge of the optic cup. — The presumptive 

 eye-rudiment of an embryo of Triton was grafted into the side of the body 



