30 BULLETIN OF THE 



on a level with the middle of the rhabdome. When it is cut very close 

 to its distal end, the nervous axis is seen to lie almost next the rhab- 

 dome. I have never seen a case, however, in which the axis and rhab- 

 dome were not separated by a line of pigment granules. In transverse 

 sections which have been thoroughly depigmented, the distal half of 

 each rhabdome is surrounded by a great number of bodies which resem- 

 ble coarse granules (Fig. .32, /6r'.). These bodies are limited almost 

 entirely to the distal half of the rhabdome. At first I supposed that they 

 were the colorless skeletons of pigment granules, but they were easily 

 distinguished from the latter by their larger size and sharper outline. 

 It then occun-ed to me that, since these bodies were found only about 

 that portion of the rhabdome which was distal to the nervous axis, they 

 might therefore be the cut ends of the finer fibrillye into which that 

 axis had been resolved. If such was the case, these bodies were in re- 

 ality fibres, not granules. In order to determine whether they were 

 fibres or granules, I examined oblique sections of the rhabdome. Fig- 

 ure 33 is taken from one of these sections. The granular body in the 

 figure is the rhabdome, and the transverse bands are the strata in its 

 substance. The projection of the long axis of the rhabdome in this 

 figure would be a vertical line. Tlie lower end of the figure is proximal, 

 the upper end distal. Owing to the fact that the rhabdome is cut 

 obliquely, what is seen at its proximal end belongs on one side of it, 

 and what is seen at its distal end belongs on the opposite side. The 

 first proximal dark band in the substance of the rhabdome is very 

 nearly midway between its ends. At the proximal end of the rhabdome 

 three distinct fibre-like bodies are seen. These are in reality longitu- 

 dinal sections of the greatly compressed retinulae, which have been 

 noticed in transverse sections. (Compare Figs. 15 and 18.) At the 

 distal end of the rhabdome, in place of the three retinulae, there are a 

 great number of fine fibres. The fibres occur only around the distal 

 half of the rhabdome, and I believe that in transverse sections these 

 fibres are represented by the small round bodies previously described. 

 From the distribution of these small fibres and their relation to the 

 distal end of the nervous axis, I am of opinion that they represent the 

 fibrillse of the nerve-fibre. 



The entrance of the fibres of the optic nerve into the proximal reti- 

 nulaB is of itself strong evidence that the rhabdome, not the cone, is the 

 perceptive body. This conclusion is further supported by the ultimate 

 distribution of the optic fibrillse. If it be admitted that the rhab- 

 dome is immediately concerned in the perception of light, it is only 



