Central nervous system of Tunica nigra. ale 
nerves arise from the median plane, but several, such as the small 
one near the oral end, are more lateral. Just how many very small 
nerves arise from the ganglion, it is hard to decide, because some 
nerves are composed of only a few fibers. The two central nerves 
at the atrial end are somewhat exaggerated in size in the drawing. 
There were few cases of anastomosis, at least between the larger 
trunks. Some of the branches when followed to the periphery were 
found greatly to change their shpaes owing to the position of muscle 
fibers; and not infrequently the peripheral part of the nerve becomes 
swollen to a larger mass than the proximal end. 
The end nerves usually do not come off from the terminal por- 
tion of the ganglion, but instead, at one side of the tip. Generally 
the terminal nerves and most of those from the middle of the gan- 
elion come off ventrally. The number and distribution of the larger 
nerves seem to be fairly constant in different individuals, but the 
smaller ones vary considerably. 
MercaLr (1899 and 1900) speaks of the continuation of ganglion 
cells along the peripheral nerve trunks of tunicates, sometimes in 
connection with the larger branches, but more often along the rapheal 
nerve. In none of my sections of this species have I seen nerve 
cells continued out far from the central mass along the nerves. 
As mentioned before, there is considerable variation in the 
smaller nerve trunks. The rapheal nerve, which Mercaur describes 
and figures, was recognized in a number of specimens, and near it, 
for a variable distance, a process extending out from the neural 
gland was considered to be the rapheal duct. The rapheal nerve 
was small and contained no nerve cells. In some specimens it was 
short and arose by itself near the atrial end of the ganglion. In 
another specimen three minute nerves, each with a separate origin, 
but from the same general region of the ganglion and close to one 
another, were considered as representing together the rapheal 
nerve. Some of the strands of these were found supplying muscles. 
Aside from these small branches, which were considered to be 
rapheal nerves, a rather thick mass of nervous matter (a lateral 
fold) is shown on the ventral side at the atrial end of the ganglion 
in Fig. C. This body runs out ventrally and ends abruptly, being 
inclosed in connective tissue. In cross section it looks like the little 
dorsal projection shown by Mercaur (1900) in his figure of Phal- 
lusia and labeled ,,ganglionic cord“; or like the figures in his 1899 
publication, his Figs. 2, 3, 4 and 5 showing the conditions in 
