12 WILLIAM H. F. ADDISON AND HAROLD W. HOW 



Eight-day rat 



At this stage the process of separation of the hds may be 

 regarded as definitely beginning, inasmuch as the form and 

 measurements of the junction epithehum are distinctly altered 

 (fig. 10). The shapes of the Hds themselves are also modified 

 at their margins. Under low-power magnification, it is seen 

 that the width of the lid nearest the junction is distinctly thinner 

 than the rest of the lid and that each lid tapers to its narrowest 

 point at the place of junction with the opposing lid. The form 

 of the junction epithelium is altered chiefly by reason of the 

 deepening of the outer groove. The measurements are now 

 21 Cm X 50 n, and if these be compared with the preceding stage, 

 it is found that the conjunctival-epidermal length has decreased 

 and the interpalpebral distance has increased. Thus it is seen 

 that while the epithelial proliferation at the margins of the lids 

 continues and new cells are being constantly added, the effect 

 now is to thicken the marginal epithelium on each lid, and not 

 to increase the conjunctival-epidermal dimension, as measured 

 in its midline. There are still a few marginal fol icles attached 

 to the junction epithelium which are solid cylinders of cells, and 

 consequently have not advanced to the stage of canalization and 

 do not contain hair shafts (fig. 10, h). The rest of the folHcles 

 at the margins which are attached to the free epithelium are 

 conspicuously long structures, containing hair shafts which pro- 

 ject beyond the epidermis. It is noticeable that the cells of the 

 midline of the junction epithelium are very pale staining, as 

 compared with cells in a similar position in the preceding stage, 

 and this change in appearance indicates that they are about 

 to become keratinized. 



Nine-day rat 



The length of the junction epithelium in the direction of the 

 line of fission is only about half what it was at eight days, now 

 measuring 108-126/x (fig. 11). This difference is principally by 

 reason of the increased depth of the epidermal groove. The 

 interpalpebral distance at the narrowest region of the epithe- 



