85 



where most of the characteristic dark brown retinal 

 pigment is collected (fig. S6, Pig.) ; and (3) the basal 

 resrion, which is external to the basal membrane, and 

 is continued outwards into fine nerve fibres continuous 

 with the nerve cells of the optic ganglion. The nucleus 

 also is found in this region (fig. So, Opt. N. f. ; Ret. N.). 



There are two long slender cuticular rods in each 

 retinal cell. These are crescentic in cross section, and 

 enclose between them the cytoplasm of the cell. By 

 making a cross section of the retina, i.e., at right angles 

 to the length of the cells, it will be seen that the rods 

 are arranged in groups of four, all four belonging to 

 adjacent but separate cells. Hence the two rods of any 

 cell belong to adjacent groups of four rhabdomes. 



The limiting cells lie between the visual or retinal 

 cells. They are broadest at the base, and the roundish 

 nucleus is situated here. Also in this region there is an 

 accumulation of pigment granules, corresponding to that 

 in each retinal cell (PI. X, fig. 86, Lim.N.). The 

 limiting cells are shorter than the visual cells, and end 

 just internal to the basal membrane (fig. 86, BJtf^). 

 This is a membrane of connective tissue, external to the 

 limiting cells therefore, but pierced by the retinal cells. 

 The region below this membrane and between the basal 

 part of the visual cells is occupied by connective tissue 

 and blood vessels (fig. 86, C. T.). In the region where 

 the rods are found the limiting cells extend forward only 

 as very fine protoplasmic processes (fig. 86, Lim x CJ, 

 which are continued as far as, and secrete, the membrana 

 limitans, which covers the internal surface of the retina 

 (fig. 86, M. L.). 



Hesse has observed in E. moschata a fine, somewhat 

 sinuous fibre which runs centrally down each retinal cell, 

 from the basal region, and ends in a minute knob at the 



