No. I.] SYMPATHETIC GANGLIA OF VERTEBRATES. 57 



thetic cell before breaking up into secondary branches. The 

 number of such spirals and their arrangement are subject to 

 much variation. In Fig. 14 an axis-cylinder with four spiral 

 turns is shown. In Fig. 1 5 is shown a long spiral, which sur- 

 rounds a long and straight process of a unipolar sympathetic 

 ganglion cell. In PI. IV, Fig. 17, we may see a portion of four 

 pericellular plexuses ; special attention is, however, drawn to 

 the one in connection with the axis-cylinder showing the spiral 

 turns. The spiral fiber, a, here shown is a collateral branch 

 of a medullated fiber, a' ; the collateral branch, after making 

 many turns around the process of the enclosed sympathetic 

 cell (the process and cell body of the sympathetic cell are not 

 shown in the figure ; they can, however, be quite clearly made 

 out in the section), breaks up into a number of fine varicose 

 fibrillae, which form the pericellular plexus. Attention needs 

 further to be drawn to the network of fine fibrillae seen within 

 the spiral fiber. Many of these fine fibers branch from the 

 spiral fiber. Their arrangement is, however, so complex that 

 they can be followed for only a short distance. Such intra- 

 spiral fibers were seen only a very few times, when the prepara- 

 tions seemed very well stained. They form a network which 

 is in very close proximity to the straight process of the enclosed 

 sympathetic cell, and suggest the possibility that the process 

 may be stimulated directly through the intra-spiral fibrillae. 

 This figure shows further some very small varicose fibers {c), 

 which enter the spiral from without. Where these fibers come 

 from, and the nature of their ending, I have not been able to 

 ascertain. I should like to suggest that such fibers may be 

 sympathetic fibers ending on the sympathetic cell or on one of 

 its large processes. I possess, however, very few observations 

 that would tend to strengthen such a view. My reason for 

 suggesting the hypothesis is based on the fact that, in birds 

 and Mammalia, end branches of sympathetic fibers would in 

 some cases seem to end on dendritic branches of other sym- 

 pathetic cells, as will be stated in the following pages. In 

 PI. IV, Figs. 14-16, only the spiral fiber and the pericellular 

 plexuses are shown ; their arrangement and structure are 

 more easily seen when the other parts of the ganglion are 



