488 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



EXPERIMENTAL LENS INDUCTION IN DIFFERENT SPECIES 



In the earliest experiments with Rana fiisca as material neither lens 

 development nor the loss of epidermal pigment characteristic of corneal 

 development occurred when the presumptive optic region was removed at 

 the stage of early neural plate, and a similar dependence of lens formation 



Fig. 162, A-C. — Stages in development of amphibian lens. A, early optic cup; r, retinal; 

 t, tapetal layer; and /, epidermal thickening of early lens development; B, C, later stages, in C 

 formation of fibers beginning (schematized after Rabl, 1898). 



on presence of optic cup in other vertebrates seemed probable (Spemann, 

 1901a). But lack of uniformity soon became evident: lenslike structures 

 were found to develop in R. palustris after killing the optic primordium 

 (King, 1905); further experiment showed that a well-formed lens with 

 fibers may develop in R. esculenta after removal of the optic region from 

 the neural plate; also, in Bombinator, R.fusca, and R. cateshiana apparent 

 beginnings of lens development (lentoids) sometimes appear in similar 



