EYE 



139 



Sclerotic, Cornea, Choroid. — These portions of the eyeball 

 are gradually differentiated out of mesenchyme which becomes 

 concentrated round the primary parts of the eye. In the case of the 

 cornea the first stage in the developmental process consists in the 

 accumulation between lens and ectoderm of a clear jelly-like secretion 



Ftg. 77.— Variations in the early stages of the development of the Lens. 

 A-E, PHstiu'rus ; F-I, Siredon (after Rabl, 1898) ; J, K Phyllomedtisa (after Budgett, 1899). 



continuous, and identical in character, with that which fills the 

 optic cup. 



As development goes on (Knape, 1909), a thin layer of this 

 jelly-like material, about midway between the lens and the ectoderm, 

 becomes condensed to form the rudiment of Descemet's membrane. 

 Amoeboid cells from the mesenchyme round the optic cup creep 



