PLATE 2 



EXPLANATION OF FIGURES 



Drawings of series of sections across junction epithelium of eyelids of albino 

 rats at various ages, from nineteen days fetal stage until twelve days after birth. 

 In all, the skin surface of the lids is shown toward the top of the page. X 160. 



6 Nineteen-day fetus. Eyelids fused together by their epithelial margins; 

 (cp) groups of epithelial cells, which formed the projecting marginal ridges of 

 epithelium in the approximating lids (fig. 5), and which have been turned aside 

 by the lids pressing close together; (/t) beginning development of hair follicle 

 at outer angle of lid. 



7 Twenty-one-day fetus. Increased thickness of junction epithelium in 

 conjunctiva-skin direction; hair follicles (h) developing at outer angle of lid and 

 on skin surface; (t) epithelium at inner angle of lid beginning to proliferate to 

 form tarsal gland. 



8 At birth. Junction epithelium somewhat decreased in longest diameter; 

 hair follicles (h) in different stages; (k) keratohyalin granules very distinct in 

 cells at outer surface of junction epithelium. 



9 Four-day. Junction epithelium increased in length; (h) hair follicle buds 

 beginning from middle of junction epithelium; a hair shaft is seen projecting 

 through skin of lid; granules (A:) of stratum granulosum very evident. 



10 Eight-day. A distinct groove on outer surface where lids join; (/) cells 

 of alveoli of tarsal glands are differentiating, but duct is still solid cord of cells; 

 (h) young hair follicles developing from epithelium near outer angle of lid; (s) 

 sebaceous glands of older hair follicles, which open on the skin surface. 



11 Nine-day. The epidermal interpalpebral groove has deepened; {t) ducts 

 of the tarsal glands are canalized. 



12 Ten-day. A groove has appeared also on conjunctival side of junction 

 epithelium; (/i) hair follicles and developing sebaceous glands; (t) alveoli of tarsal 

 glands; keratohyalin granules are seen not only in cells of epidermal groove, but 

 also in junction epithelium and in cells lining conjunctival groove. 



13 Twelve-day. Area of epithelial junction is much lessened and shows ker- 

 atohyalin granules throughout; point of attachment of ducts of tarsal glands (0 

 is now opposite last remaining conjoined epithelium; owing to this diminution 

 of the junction epithelium, the hair follicles which developed from it now open 

 upon the epidermal surface of the lid. 



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