DEVELOPMENT OF EYELIDS OF ALBINO RAT 13 



lium is practically the same as before, 50m. The ducts of the 

 tarsal glands show a well-defined lumen in the region near 

 where the duct epithelium is continuous with the junction 

 epithelium, but they have as yet no outlet to the outside. The 

 alveolar out-pouchings of the glands are becoming well devel- 

 oped and their glandular cells begin to show their characteristic 

 pale-staining mature appearance (fig. 11, t). By this time all 

 the immature hair follicles which were seen at seven days attached 

 to the junction epithelium now show hair shafts beginning to 

 grow out. In the interval since seven days, however, the epi- 

 dermal groove has also deepened so that the outlet of the hair 

 follicles now open into it, and the hair shafts grow through the 

 epithelium of the outer margin of the lid, not into the junction 

 epithelium. There is, in a way, a process of eversion of the 

 growing margin of each lid, which goes on all through the stage 



of separation of the lids. 

 « 



Ten-day rat 



Both the inner conjunctival furrow and the outer epidermal 

 groove have become deepened, and in consequence the junction 

 epithelium as measured between the two depressions is now 

 reduced to a thickness of 90m. In the epithelial cells lining the 

 conjunctival furrow are now seen for the first time keratohyalin 

 granules. These are in the form of small deep-staining par- 

 ticles, arranged in a linear fashion in the flattened, superficial, 

 four or five rows of cells. The deepest layers of these cells at 

 the bottom of the furrow come into a close relation with similar 

 cells of the epidermal groove. The result is that keratohyalin 

 granules are seen practically all through the midHne of the 

 junction epithelium. This represents a definite stage of advance 

 in the disjunction process, inasmuch as it shows active progress 

 in the keratinization of these cells. The interpalpebral distance 

 is about 75fJL at the narrowest region, and this is a considerable 

 increase as compared with the nine-day measurement of 50;u. 

 Although the lumina of the ducts of the tarsal glands are widely 

 open even up to the marginal epithelium, no patent outlets were 

 seen. The hair follicles at the margin of the lids have all attained 



