THE LATER DEVELOPMENT OF THE FROG 



147 



D 



FIG. 50. The development of the eye in the Urodele, Siredon pisciformis. 



Lfter Rabl. A. Of embryo with about twenty-five pairs of somites, showing the 



dckening of the lens rudiment. B. Invagination of the lens and formation 



the optic cup. C. Lens separating from the superficial ectoderm in an embryo 



about thirty-five pairs of somites. D. Thickening of the inner wall of the lens. 



Shortly before hatching; differentiation of the rods and cones in the retinal 



rer. a, Anterior chamber of eye; c, cavity of primary optic vesicle; co, cornea; 



ectoderm of head; /, choroid fissure; i, inner or retinal layer of optic cup; 



, rudiment of iris; k, optic stalk; I, lens; o, outer or pigmented layer of optic 



;up; p, posterior chamber of eye. 



