''***(^P»-T**»> 





'.^^^^^ ^7-> »• "I, ''"?'^"'' > .'■' 



.^^ 



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. Pr. 



J Li'* 





Fig. 21 



The dependence of lens-differentiation on the optic-cup in Triton, a, Larv^a into 

 which at the mid-gastrula stage a piece of presumptive brain region from another 

 embryo of the same age was grafted. The graft (g.) developed by self-differentia- 

 tion into parts of the brain, and an eye-cup which induced the formation of a lens 

 (/.) from the ventral trunk epidermis of the host, b, Section through the same 

 larva showing (v.) the vesicle formed from host tissue and containing the graft; 

 br. portion of grafted brain ; e. grafted tissue differentiated into eye-cup ; Nr. spinal 

 cord ; Pr. pronephric tubules, of host embryo. (From Mangold, Arch. Entwmech. 

 cxvii, 1929.) 



