THE EMBRYOLOGY OF THE EYE. 35 



formed it is surrounded by a capsular mem- 

 brane which gradually increases in thickness. 

 It is to be considered a cuticular formation of 

 the epithelial cells, and it becomes much 

 thicker anteriorly where the epithelial cells 

 remain permanently. Anteriorly also it may 

 be split up into lamellae, each of which repre- 

 sents in all probability a certain period of 

 formation. The vascular sheath is for the 

 nutrition of the lens during its rapid growth, 

 and seems to play no role in the formation of 

 the capsule (cf. p. 20). 



5. Cornea. — When the lens-sac becomes 

 separated from the external epiblast, an open 

 space remains between the two (Fig. 6). In 

 the rabbit (Fig. 4) the mesoblastic tissue 

 passes over the margin of the secondary optic 

 vesicle into the cavity of the latter. This 

 mesoblastic tissue contains many vessels, and 

 at this stage both the anterior space and the 

 cavity of the vesicle are filled with a fluid 

 which is probably transuded from the vessels. 



Mesoblastic cells now push out from the 



