Differentiation of lens- and Iris-like tissue in explants of the anterior part of the frog neural plate.

The differentiation was studied of presumptive eye material developing in the absence of ectoderm. Explants were made of the anterior (forebrain- and eye-forming) part of the neural plate, without the lateral neural folds, of early to mid-neurulae ofRana temporaria andR. esculenta. The underlying endomesoderm as well as the outer layer of the neural plate were removed prior to explantation. Consequently the explants did not become surrounded by epidermis. The explants segregated into a mass of forebrain tissue and a single retina, which did not assume the typical cup shape. In between these two components an interzone developed, consisting of incompletely differentiated layers of iris tissue. In the interzone typical lentoids, as well as lentoids continuous with other tissue components, differentiated. The formation of lentoids in the absence of ectoderm is discussed in terms of the availability of a lens-inducing agent. It is assumed that in the interzone the lens-inducing agent acts on tissue components which are competent for lens formation. The formation of lens-like tissue may be regarded as analogous to lens regeneration in newts.