48 FT. M. BERNAEl). 



Paet V. 



On the Removal of the Absorbed Pigmentary 

 Matter from the Rods: an Explanation of the 

 '^Miiller's Fibres/' 



In Part II I described in detail a set of phenomena which 

 found their simplest interpretation in the assumption that 

 the protoplasmic vesicles, known as the rods, protruded by 

 the retina against the pigmented epithelium, absorbed the 

 pigmented granules, and at times also the cytoplasm of the 

 pigment cells. I propose in this paper to describe another 

 set of phenomena which indic;ite the way in which the rods 

 are freed from the excess of matter thus absorbed. 



My results differ somewhat widely from any hitherto pub- 

 lished, and especially from those obtained by the now popular 

 impregnation methods, and I ought, perhaps, to make some 

 excuse for not testing those other methods myself. My 

 answer, I fear, can only be an apology. I selected the 

 purely comparative method deliberately as the only absolutely 

 cei'tain way of obtaining light on intricate morphological 

 problems, but the method is slow and laborious, and I grudge 

 the time necessary to become an adept in the use of others, 

 the results of which have still to be interpreted. 



The pigmented matter was, as we saw, absorbed through 

 the walls of the outer limbs, and some of it found its way 

 through the transverse membranes into the inner limbs, 

 where it helped to form the bodies known as the ellipsoids. 



Part of the absorbed matter, then, finds its way through 

 the transverse membrane into the inner limb. Here, unless 

 it can find some furtlier method of escape, it must accumulate 

 and cause the inner limb to swell. No such swelling of 

 the inner limb takes place in the Amphibia, but it is a 

 striking phenomenon in many fish. This is the explanation 

 of their " giant cones " which are so startling when seen for 

 the fii'st time (see figs. 20, J), and 21). 



