40 THE EMBRYOLOGY OF THE EYE. 



of the corneal development. But after the 

 rudimentary cornea is a few cells deep, the 

 anterior cells lie directly on the epithelium. 

 In birds the stroma-cells do not reach the 

 epithelium at any period. 



There has been much discussion as to 

 whether the corneal cells are cells which have 

 wandered in from the mesoblast, or whether 

 they have been produced in loco. Some 

 authors have described the cornea as consist- 

 ing in the beginning of a non-cellular homo- 

 geneous material into which the corneal cells 

 pass by migration. Others have described it 

 as a homogeneous material containing a few 

 cells which by their division produce the cor- 

 neal cells. In mammals, the homogeneous 

 material need not be taken particularly into 

 account. It is in all probability simply an in- 

 different fluid filling a cavity. The mesoblas- 

 tic cells at the sides proliferate and thus a thin 

 layer of cells is pushed through the cavity. 

 The cells of this layer and the cells at the 

 sides continue to proliferate and form the 



