THE THIRD DAY, [CHAP. 



FIG. 52. 



SECTION THROUGH THE EYE OF A FOWL ON THE EIGHTH DAT 

 OF DEVELOPMENT, TO SHEW THE IRIS AND CORNEA IN THE 

 PROCESS OF FORMATION. (After Kessler.) 



ep. epiblastic epithelium of cornea ; cc. corneal corpuscles growing 

 into the structureless matrix of the cornea ; dm. Descemet's 

 membrane ; ir. iris ; cb. mesoblast of the iris (this reference 

 letter points a little too high). 



The space between the layers dm. and ep. is filled with the 

 structureless matrix of the cornea. 



through the structureless corneal layer, and divide it 

 into two strata, one adjoining the epiblast, and the 

 other adjoining the inner epithelium. The two strata 

 become gradually thinner as the corpuscles invade a 

 larger and larger portion of their substance, and finally 

 the outermost portion of each alone remains to form 

 above and below the membrana elastica anterior and 

 posterior (Descemet's membrane) of the cornea. The 

 corneal corpuscles, which have grown in from the sides, 

 thus form a layer which becomes continually thicker, 

 and gives rise to the main substance of the cornea. 



Whether the increase in the thickness of the layer is 

 due to the immigration of fresh corpuscles, or to the 

 division of those already there, is not clear. After the 



