In the experiments of Lewis (1904) with Rana palustris mentioned on p. 16, it appeared that heterotopically transplanted optic vesicles elicited lens formation in ectoderm that does not normally form lens. However, it was not possible in these experiments to distinguish with certainty whether the ectopic lenses had been formed by host ectoderm or by the transplanted optic vesicle - or any donor tissue adhering to the optic vesicle. Recent investigators have added a design feature to overcome this uncertainty. What kind of design feature do you think they used? Why was this reinvestigation important? Click here for the answers.
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