NERVOUS SYSTEM OF PHORONIDA 385 
The central nervous system was demonstrated as a more or 
less semicircular band which was not very wide. Some scattered 
cells in the central nervous system and at the bases of the ten- 
tacles seemed to be true nerve cells. All over the surface of the 
body little groups of stained cells are the sense cells. These are 
similar to those which Retzius describes in some invertebrates. 
In the body the sense cells were not as well seen as in the tentacles 
because of the thick opaque regions where they occurred. The 
stain was especially valuable in distinguishing the sensory cells 
in the tentacles and in little groups over the surface of the body. 
Some nerve strands and cells together with a portion of the 
central nervous system were merely indicated. More intense 
stain added nothing to the knowledge of the nervous system; on 
the contrary, the coloration of connective-tissue cells and others 
obscured the results obtained with nerve tissues. 
The central nervous system of Phoronis pacifica is much like 
that described in other forms. It has its chief concentration a 
little below the level of the anal opening and the nephridia. 
This thick part of the nervous system is directly continuous 
with the epithelium of the surface of the body and dorsal to the 
anal papilla, and about the depression caused by it. From here 
the thickening passes towards the tentacles with fibers to them 
and to the lophophore. Between the depressions on each side are 
the chief thickenings of the nervous system. Although this 
central part is continuous with the epithelium, there are distinct 
nerve cells and fibers. At this greatest thickening there are 
three chief cell centers among the fibers. There is quite a 
thickness of nervous tissue about each depression of the lopho- 
phore. On the left side near the lophophore is the beginning of 
the clear cord of unknown function first noted by Caldwell. It is 
partly surrounded by cells and runs ventrally until it passes 
through the basement membrane of the body-wall and comes to 
be just under the epithelium. It runs the length of the body in 
this position, becoming smaller and smaller. It does not seem 
to be of nervous tissue, although it is directly connected with 
the nervous system. 
