46 H. M. BERNARD. 



On looking at these our attention is at once arrested by- 

 figs, a — c. We have apparently typical cones with their 

 points thrust into terminal vesicles. A little reflection^ how- 

 ever, shows how such appearances could be easily produced 

 as transitory phases. To n:ahe it clear I give a diagrammatic 

 seriesj fig. 14, a — d. a represents an unmodified vesicle 

 protruded as a long oval. The pressure caused by the 

 gradual protrusion of new vesicles will be exerted upon a in 

 the direction of the arrows shown in h, with the result 

 that a will take the form shown by h (cf. the middle vesicle, 

 fig. 12). In the narrow neck oE h staining matter accumu- 

 lates. Continuation of the pressure further lengthens the 

 neck, and at the same time the adding of new vesicles forces 

 back the pigment cells. ^ 



In the stage c I have introduced a refractive globule, 

 which we may assume to have come out of the distal 

 vesicle as matter absorbed by it from the pigment, as ex- 

 plained at length in Part II, At this stage it is again the 

 turn of the element whose form-changes we are following to 

 receive another discharge from the retina or, as argued in 

 Part II, from its nucleus. This discharge drives out the 

 staining matter which occupied tlie neck, so that it protrudes 

 into' the distal vesicle. The three figures 13, a — c, show 

 three distinct degrees of thrust, quite accidentally selected, 

 the figures having been drawn in the order shown in the 

 plate before I was at all clear as to their meaning. In a, 

 only the narrow tip of the matter from the neck has been 

 pushed into the sac; in c, the tip and a portion of the 

 refractive globule, in this case the matter composing the tip 

 itself has been disarranged against the distal end of the 

 vesicle; in h, a larger portion of the staining matter still has 

 been thrust outwards into the sac. These curious "cones," 



' This Icnf^lhening of the vesicles widens tlie distance between the pigment 

 layer and tlie body of the retina. The width is greatest in the centre of the 

 relina, and in very young eyes diminishes rapidly on cither side. Tliis is 

 certainly due to tiie greater activity of vesicle formation, i. c. of rod-produc- 

 tion in the area of most active functioning. 



