1914] Lil tie: Ocelli of Pol ijorch is 315 



Under higher magnification the ocellus (pi. 14, fig. 4) reveals 

 a great differentiation in its cellular structure. The pigment 

 cells (r. pig. c, and br. pig. c.) are the most conspicuous and 

 occupy about half the entire eye. They are four to five times 

 as long as broad, are somewhat rounded at their periphery, while 

 the inner ends are drawn out more or less to a blunt point. They 

 are arranged radially, from the inner surface of the depression. 

 Those situated centrally extend from the bottom of the lens 

 almost to the basal membrane below. All bear a nearly spherical 

 nucleus at their inner ends just before they begin to taper. The 

 nucleus is sometimes masked by the abundance of pigment which 

 is found distributed throughout the cells, being denser towards 

 their upper ends than towards their lower ones. These cells are 

 not placed in close conjunction with each other but small spaces 

 are left between them which are filled by the projections of the 

 spindle or club-shaped retinal cells {ret. c.) which alternate with 

 the pigment cells. These correspond to the so-called "Sehzelle" 

 of the Hertwigs (1878). They are not all uniform in shape, those 

 near the center being somewhat larger and le-ss spindle-shaped. 

 The long, narrow neck which reaches up to the base of the lens 

 suddenly widens below the pigment cells into the broad, rounded 

 portion of the cell, and then either rounds off abruptly or tapers 

 to a more or less pointed end. This pointed end is more charac- 

 teristic of the outer than of the deeper cells. The latter may 

 often be bent at quite an angle to the neck portion. The nucleus 

 is larger than that of the pigment cells and is situated at the 

 widest part of the cell. This makes this layer of large nuclei 

 come at a lower level than do the smaller ones of the pigment cells. 



The sensory cells and pigment cells give place peripherally to 

 the modified epithelium of the eye {ep.c). Throughout the 

 entire surface of the eye outside of the lens this type of cells is 

 found. They vary slightly as to size and general shape, but on 

 the whole maintain a fairly uniform structure. They are broad 

 at their periphery, which ends in the thin cuticle above them, and 

 then gradually taper to a long drawn-out point, always pointing 

 away from the surface of the eye. The resemblance between 

 the pigment cells and this peripheral sensory epithelium is so 

 close, and the one blends so evenly into the other, that the pig- 



