THE LATER DEVELOPMENT OF THE FROG 147 



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

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

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

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

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

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

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

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

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

 cup; p, posterior chamber of eye. 



