256 



BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



which lie nearer to the eye of the observer have been arbitrarily repre- 

 sented as darker than more remote ones. This remark does not apply 

 to the nuclei. 



Ordinary sections. Except in the region of the rods, the sensory cells 

 of the retina, when fixed in any ordinary solution (e. g. Flemming's) and 

 stained with haematoxylin, do not show fibrillae. In the rods, however, 

 they are very easily demonstrated. Hesse has recently described them 

 for this region and given a text figure of the rod of Limax. He demon- 

 strated that essentially the same relations obtain as in the rod of Helix, 



whose retina he (:02 b ) has so well illustrated. 

 (See Fig. C, p. 237.) Proximal to the rod 

 the fibrils have not been traced hitherto. I 

 shall describe the rods first, coming subse- 

 quently to the more proximal parts of the cell. 

 Figure 21 (Plate 3) shows in cross section 

 five rods. In the spaces between them is 

 the vitreous humor, which envelops the man- 

 tle. The rod-axis contains many distinct 

 fibrils. In strictly cross sections, they usu- 

 ally appear at any given focus like so many 

 granules. But if the section is in the least 

 oblique, their fibrillar appearance is unmis- 

 takable. Sometimes the fibrils are grouped 

 near the centre of the rod-axis and have 

 a slight twist, so that on focusing they sug- 

 gest the strands of a loosely twisted rope. 

 Sooner or later the distal part of each fibril . 

 turns to the periphery of the rod-axis and ends 

 immediately under the surface of the core 

 in a little knob or knot (Fig. D, and 

 Plate 4, Fig. 49, cp. trm.), which Hesse has 

 likened to the basal body in a ciliated cell. 

 For this structure I suggest the name end-body, as being a conveni- 

 ent, purely morphological term, without prejudice as to the homology 

 or function of the part. The end-body marks the distal limit of the 

 fibril within the cell ; but from the end-body there arises a little tuft of 

 much finer fibrillae, which pass through the surface of the core where 

 they become the fibrillae of the mantle, already described. Unless the 

 fixation is perfect, the mantle fibrils seem to cohere with one another 

 more or less, so that they appear coarser than they really are. This 



rdl. 



Fig. D. Diagrammatic view 

 of a group of retinal cells of Limax 

 maximus. For explanation of 

 abbreviations, see p. 283. 



