PLATE 10 



EXPLANATION OF FIGURES 



Microphotographs of horizontal sections through the head of the sparrow, 

 showing different stages in the development of the eye. Ap, annular pad of 

 lens; Br, brain; C, cornea; Ch, chiasma; Chr, chorioid; E, ectoderm (epithe- 

 lium) ; L, lenticular portion of lens; Lc, lenticular chamber represented by a line; 

 Ld, lid; M, developing eye muscles; N , nictitating membrane; Op, optic nerve; 

 P, pecten; Pg, pigment layer of retina; R, retina; Scl, sclera. 



63 Embryo of 7f days, showing the development of the nictitating mem- 

 brane and lid. X 20. 



64 Embryo of 8 days. Shows advancement in development of nictitating 

 membrane, retina, lens, and eye muscles. X 40. 



65 Same series as figure 64, but at a different level. A portion of the optic 

 stalks close to the brain is seen at Op. The internal and external rectus muscles 

 can be identified. X 40. 



66 Same series as figure 64 at the level of the dorsal edge of the optic nerve 

 entrance. X 40. 



67 Same series as figure 64 through the most prominent part of the develop- 

 ing pecten. At this stage the pecten appears as a conical mass of cells arranged 

 in the form of a ridge along the extent of the nerve entrance. X 40. 



68 Same series as figure 64 through the optic chiasm. X 40. 



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