IX 



MOLLUSCA 



367 



projects inwards as a rod -shaped structure. The cells forming 

 this part of the wall of the eye -sac are enlarged and cubical, 

 whilst those forming the more peripheral portions of the eye-sac 

 wall are small. The large cells, which secreted the 'primary 'part of 

 the lens, disappear in the centre, probably as a result of lens secretion ; 

 towards the sides they persist as the characteristic cells of the corpus 

 epitheliale of the ciliary body. The further growth of the lens is 



o.st. 



cep 



o.st 



FIG. 300. Transverse section of the eye of a nearly ripe embryo of ,SV///f <>/ 



( After Faussek.) 



c.ep, epithelial body; c.ujji, small cells nf r.rp forming lens capsule; <:f, conical fold constituting 

 the outer wall of the outer chamber of the eye; K.I, thickening, the rudiment of the lower eye-lid ; 



g.C, ganglion cells of the retina; i.rli, inner chamber of tl ye; i.l, inner segment of the lens; h; 



iris; o.efc, outer chamber of the eye; o.l, outer segment of the lens ; u.xt, eye-stalk; v.c, visual cells nf 

 the retina ; n-.li, nicsodernuil rudiment nf the white body. 



effected by means of the small cells forming the more distant portions 

 of the wall of the eye-sac. These cells grow forward on each side 

 towards the lens, as a kind of fold overspreading the large cells of the 

 corpus epitheliale; and by them the lens is added to, both in thick- 

 ness and depth. 



The iris folds and the outer segment of the lens are formed before 

 the fold which walls in the anterior chamber of the eye, and constitutes 

 the corneal fold, is formed. The outer segment of the lens is formed 

 like the inner segment ; at first it is a cuticle which thickens in the 



