THE EMBRYOLOGY OF THE EYE. 39 



in the chick with a homoo^eneous non-cellular 

 material, and the mesoblastic cells which push 

 out to form the stroma of the cornea do not 

 rest directly on the posterior surface of the 

 external epithelium, but lie a little distance 

 from it. A layer of the homogeneous material 

 remains between them, and this soon appears 

 as a double-contoured membrane which is 

 permanent. The epithelium often cannot be 

 stripped off it cleanly, and fragments of the 

 cells remain adherent to the membrane. This 

 homogeneous material is probably a transu- 

 dation from the vessels. The mesoblastic 

 cells push out into it, and for a time it forms 

 the intercellular matrix of the cornea. 



The process occurring in birds has been 

 supposed by many to hold good for mammals. 

 In my opinion the development of Bowman's 

 membrane is entirely different in the two. 

 The first stroma-cells of the cornea in mam- 

 mals have been often described and pictured 

 as lying some distance behind the epithelium. 

 This may sometimes be found at the beginning 



