68 Journal of Entomology and Zoology 
level of the anal opening and the nephridial tubules. This thickest 
portion of the nervous system directly continues with the epithelium 
of the surface of the body and is dorsal to the anal papilla in the 
depression caused by the anal prominence; from here the thicken- 
Ing passes toward the tentacles sending fibers to the lophophore and 
the tentacles. The lophophore depression on each side marks off 
the chief thickening of the nervous system. This central part, 
although continuous with the epithelium is made up of a distinct 
mass of fibers and cells. At this point three chief centers of cells 
are found among the fibers while out laterally strands run to the 
lophophore depressions and out to the tentacles. There is quite a 
mass of fibers and cells in the region of the lophophoral depression. 
Running out vertrally on the left side just medial to the lophophoral 
depression and between it and the left nephridium is the clear cord 
of unknown function noticed first by Caldwell. This cord sur- 
rounded partly by cells comes to run farther ventrally until it 
passes through the basement membrane of the body-wall and comes 
to lie just under the epithelium. This end does not seem to be of 
nervous tissue, although it is connected with the central part of the 
nervous system. 
If I understand Torrey’s description aright his material must 
have been too poorly fixed to show the relationship of the nervous 
system for in well preserved specimens the cerebral nervous sys- 
tem is continuous laterally with the lophophoral organs as well as 
with any lateral or longitudinal extensions of the nervous system. 
My observations both on Phoronis and Phoronapsis agree closely 
with those of Pixell. In Phoronapsis the central nervous system 
seems more elongated, as Pixell found. 
With the exception of the central part of the nervous system 
the nerve cells are not clearly different from the epithelial cells, but 
careful study shows at the bases of the cells as well as farther down, 
nerve cells with their fibers directed into the basal mass of fibers. 
In the epithelium are bipolar cells, some of which may be sensory, 
although many of the prominent strands are those of supportive 
cells. 
ACTINOTROCHA. 
It seems best to consider the larval stage of Phoronis briefly 
at this place. Schneider, 1862, in his discussion of the develop- 
ment of Actinotrocha does not consider the nervous system. Cald- 
well has the first work of importance but his account, according to 
MacBride, implies that the apical plate and adjacent ganglion of 
the larva are lost, and the cerebral ganglion of the adult must be a 
new structure. But in every trochophore so far studied the apical 
plate with its ganglion forms the material which persists to the 
adult condition. 
