PLATE 14 



EXPLANATION OF FIGURES 



Microphotographs of sections of the sparrow eye to show the development of 

 the different structures. Ap, annular pad of lens; C, cornea, ; Cp, ciliary process; 

 F, area and fovea centralis; Hg, Harder's gland; I, iris; L, lower lid; LI, upper 

 lid; Lg, lacrimal gland; Op, optic nerve; OpT, optic tract; P., pecten. 



81 Horizontal section through the head of an embryo at the age of 13 days 

 ]^the age of hatching) along the plane <S'-*S' of figure 15. The relation of the optic 

 tracts, chiasma, nerves, and pecten is shown. The pecten shows a more flattened 

 appearance, having almost completely lost its conical shape, but is in no way 

 folded. X 10. 



82 Vertical section through the center of the right eye of a young sparrow two 

 days after hatching and before the eyes have opened. The complete closure of 

 the lids is noticed. X 20. 



83 Horizontal section through the center of the left eye of a young sparrow 

 2 days after hatching. The fovea and area centralis show very little differentia- 

 tion. There is a slight thinning of the retina at F. All the layers of the retina 

 are more definite, but the rod-and-cone layer. These latter elements appear 

 as slight jjrojections from the outer nuclear layer. X 10. 



84 Same series as figure 83 passing through the nerve entrance at a lower 

 level. The pecten now shows some of the characteristic folds found in the adult. 

 The layers of the retina are more sharply defined except the rod-and-cone layer. 

 X 10. 



85 Vertical section through the right eye of a young sparrow 4 days after 

 hatching. The lids are now seen to be partly opened and the iris, the ciliary 

 bodies, the annular pad, and chamber of the lens are well defined. The section 

 passes a little to one side of the developing fovea. The rods and cones now apjiear 

 as conical projections about one-fourth the length of the adult. X 10. 



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