162 A. B. DAWSON 



dence concerning their possible continuity with intra-epi dermal 

 fibers is lacking. In no case, however, was there any evidence 

 of a peripheral bundle of fibers (Kowalski, '09) being given off 

 by a tripolar cell. In many instances numerous fibers were 

 observed running parallel with a peripheral process of a tripolar 

 cell, but they were not connected with the cell itself, and, further- 

 more, a process of a tripolar cell could usually be easily distin- 

 guished from the majority of the fibers in a peripheral nerve by 

 its coarseness and the kinked, irregular course it pursued (fig. 1). 



b. Spindle-shaped bipolar cells 



Spindle-shaped bipolar cells, unlike the tripolar cells, are not 

 restricted in their distribution. In a body segment they may be 

 found anywhere along the course of the three pairs of segmental 

 nerves, i.e., at the margin of the cord itself, along the lateral 

 nerve trunk, at the point of bifurcation of this trunk, along the 

 dorsal and ventral portions of the nerve rings running between 

 the two muscular layers, and in the peripheral nerves passing 

 through the layer of circular muscles. Near the dorsal and ven- 

 tral midbody region the bipolar cells are more often found in the 

 peripheral branches. This of course would be expected since the 

 nerve rings in this region are greatly reduced. Nearer the setae, 

 however, the number of cells found in the nerve ring gradually 

 increases and in the so-called intersetal tract small groups of cells, 

 three, four, and five, are commonly found (fig. 2). 



The spindle-shaped bipolar cells also exhibit some striking 

 variations in size (figs. 3, 4). As already noted, von Szuts ('14) 

 mentioned this as one of the characteristics by which he dis- 

 tinguished tw^o types of cells, ' intermuskularen Nervenzellen' 

 and ' intermuskularen sensorischen Ganglienzellen.' However, it 

 does not seem possible to use this as a basis of classification, 

 since a careful comparison of a large number of cells by means of 

 camera lucida measurements shows that between the two extremes 

 (figs. 3, 4) there is a nicely graded series of cells. Von Szuts 

 ('14) also described a difference in the arrangement of the neuro- 

 fibrils within the cells. He found that in the small cells, al- 



