SMITH: EYES OF PULMONATE GASTEROPODS. 259 



ably placed, it is easy to observe that the fibrils continue backward from 

 the core of the roil toward the nucleus for some distance practically 

 parallel and separate, just as in the rod. Figure 48 represents one case. 

 The section includes a little of the proximal rim of the mantle, where it 

 has less than a maximum thickness. Imagine the cell so bent that the 

 bit of mantle requires deeper focusing than the other end of the figure. 

 Dozens of dark fibrils issue from the core and run toward the wall of the 

 eve capsule. The fibrils of the mantle are indicated but faintly. 



To follow the course of the fibrils through the remainder of the cell is 

 not a simple matter. Their distribution through the cell in most cases 

 is unequal. The largest number usually lie on that side of the nucleus 

 where there is the most room. This fact is sometimes quite noticeable 

 at a magnification of two hundred diameters, even though the fibrils 

 themselves cannot be made out. Where they are most abundant they 

 produce dark spots, one or two, in the cell. This fact is shown by sev- 

 eral cells in Figure 16 (Plate 2). Seen from the side these spots are 

 elongated and might, upon casual observation, be regarded as paths along 

 which sinuous, yet separate fibrils find their way through the cell. Two 

 facts are opposed to such an interpretation. First, careful study of the 

 cells sectioned in all directions leads one to the conclusion that the fibrils 

 form a complicated network in the body of the cell. Secondly, from a 

 comparison of the size of the neurite with the mass of the fibrils in the 

 cell, or even in the axis of the rod, it is clear that the neurite cannot 

 possibly contain as many fibrils as are found in the core of the rod, even 

 if they were so closely packed as to make it practically a solid fibre. 

 There must be a great increase in the cross section of the conducting 

 material in the cell as compared with the cross section of the neurite. 

 Hence there must be either a branching or a network system of some 

 kind within the cell. Granting the difficulties in the way of distinguish- 

 ing a network from a branching system, it is my opinion, formed after 

 months of study, that in the body of the cell we have to do with a net- 

 work. Coming from the axis of the rods the fibrils, separate and sinu- 

 ous, continue down the distal part of the middle portion of the cell 

 for some distance in the same condition. But toward the nucleus the 

 fibrils pass over into a fine and complicated network, which is sometimes 

 diffused throughout the cell, but often is more or less localized. Figure 

 55 (Plate 4) illustrates a cell which lay nearly in the plane of the sec- 

 tion. The rod (the fibrils of whose mantle are not represented) is bent 

 on itself, so that it is sectioned not quite longitudinally. Immediately 

 proximal to the rod the fibrils ifbrl.) still run substantially parallel to 



