STUDIES IN THE RETINA. 41 



quantity aud of a very much darker brown. The colour is in 

 striking contrast with the reddish brown which is most 

 common over here. But this was not all ; probably in corre- 

 lation with this increase in mass and quality of the pigment 

 the rods were also different (see figs. 8^ 9, and 10), in that 

 the loDgitudiual striation is so marked that it can be seen at 

 once with a low power. Cross-sections of rods which seem 

 to be somewhat thin, 4 fx across, often tapering to 3 fx, shoAV 

 a thick, straggling, branching, and knotted strand running 

 down the axis of each rod as the representative of the axial 

 reticulum, and connected irregularly with the dark strise 

 running down the wall. Here and there the greater part of 

 the axis of the rod is taken up by a mass of dull grey homo- 

 geneous matter, in which case the axial reticulum is appa- 

 rently represented by clumps at the sides, but it usually 

 comes into view again on focussing up or down. These grey 

 masses in the rods are the remains of material absorbed from 

 the pigment granules (see fig. 8, with description). 



Apparently correlated with these strongly developed 

 staining stri^ is the fact that the rods, though very thin, are 

 comparatively speaking tough ; for, quite unlike those in our 

 own species of Amphibia, which break up so easily and 

 usually part at the junction of the inner and outer limbs, in 

 these eyes, Avhere the retina and choroid have parted, they 

 are drawn intact out of the dense pigment. 



Turning to the cones, we fortunately find that their vesi- 

 cular tips share in this greater toughness. Very many of 

 these latter, it is true, have broken down and have been 

 reduced to a granular mash which is very conspicuous, but 

 places such as those figured (figs. 9 and 10) might be 

 multiplied to any extent. The vesicles are shrunken, and it 

 is largely owing to the folds in their walls that they are 

 visible. Some seem to have clear traces of rows of dots 

 running down them which remind one of the rows of dots on 

 the longitudinal stria3 of the rods. In optical section the 

 wall of the shrunken vesicle could often be traced quite 

 plainly into that of the cone (fig. lOj. 



