^)^4 ^- k:t«hinouye. 



of cells in about two rows. It is the retiuji. Un the upper side of 

 the base of the eye there is foi'iiied ;t Jarge hollow. This makes the 

 eye stand out and at the snine time pushes it towards the siphonal 

 opening. Thus the hollow di^■ides the tip of a tentîjcle into two — a 

 prominent eye and a somewhnt triMUguhn- screen behind it. The 

 hollow corresponds in position -with the original mouth of the in- 

 vagination for the eye. Pigment is produced in mesoblast cells 

 surrounding the retinjil portion. These pigmented cells form the pig- 

 ment layer. A lumen is secondarily produced between the lens and 

 the retina. 



'I'he lens grows l)y the multiplication of cells in the direction of 

 the optic axis und assumes the shape of an ellipsoid, and consequently 

 the lumen between the lens and the retina distjppears (fig. 7). The 

 peculiar arrangement of cells in the lens begins in this stnge. 



• Late in de\elopment, the retinal portion is divided into two layers, 

 the retina ])rr)per and the choroid. Tliesc two layers are continu- 

 ous with each otlier at the cii'cnmfereiK'e. Soon after the separation 

 of the choroid from the retina, the tapetum is formed below the 

 choroitl. probalily by the secretion of the cells wliieVi constitute the 

 latter. I cannot corroborate the view tliat the tapetum is formed of 

 modified cell layers, tor even in these early stages 1 cannot find any 

 thing of a cellular nature in it. Afterwards rods are ])r(^duced from 

 the retinal cells. 



T]ie wore ahhrcnatrd process of development (see ]>. 2^1^) is 

 as follows : 



At the top of a tentacle the epithelium becomes thickened and 

 forms a little knob within (tig. 8). The little knob is next cut off from 

 the epithelium (fig. 9). In this stage a hollow is produced behind tin; 

 little knob and thus the triangular screen (fig. 9. s.) is formed. The 

 little knob cut off is spherical in form jind consists of a lew, large 



