ORGANS OF VISION. 



477 



While the lens is attaining its complete development there 

 appears a fresh fold round the circumference of the eye, which 

 gradually grows inwards so as to form a chamber outside the 

 parts already present. This chamber is the anterior optic 

 chamber of the adult. In most Cephalopods (fig. 277 C) the 

 edges of the fold do not quite meet, but leave a larger or smaller 

 aperture leading into the chamber containing the iris, outer 

 segment of the lens, etc. In some forms however they meet 

 and coalesce, and so shut off this chamber from communication 

 with the exterior. The edge of the fold constitutes the cornea 

 while the remainder of it gives rise to the sclerotic. 



The retina is at first a thick layer of numerous rows of oval 



<> 



FIG. 280. SECTIONS THROUGH THE DEVELOPING EYE OF LOLIGO 



AT TWO STAGES. (After Bobretzky.) 



///. inner segment of lens ; vl. outer segment of lens ; a and a. epithelium lining 

 the anterior optic chamber; gz. large epiblast cells of ciliary body; cc. small epi- 

 blast cells of ciliary body ; ms . layer of mesoblast between the two epiblastic layers 

 of the ciliary body; of. and if. fold of iris; rt. retina; rt". inner layer of retina; 

 st. rods ; aq. cartilage of the choroid. 



