The Central Nervous System Of 
Dolichoglossus 
WILLIAM A. HILTON 
Specimens were fixed in the living condition in mercuric chloride or other strong 
reagents and cut in series. Hematozylin stains seemed best for details. 
A study of the nervous system of this animal suggests similar structures in echino- 
derms. The surface epithelium is in many places underlaid with nerve strands. In 
some places these nerve fibers are very thick, in others only a few strands are evident. 
The epithlium of the surfaces of the proboscis, collar and body is of varying thickness 
and ciliated. Among the columnar cells there are in places numbers of modified mucous 
secreting cells or goblet cells. In some places also there are specialized nerve or 
sense cells which are modified epithelial cells whose processes are slender and run as 
nerve fibers below the layer of nuclei. Multipolar cells also occur. 
We may speak of the nervous system as being the lower fibrous layer of the epithe- 
lium in many parts of the body. This central nervous system is especially thickened 
on the dorsal side of the body, particularly at the junction of the proboscis and collar 
and also under the collar on the dorsal side. The part which might be called the 
brain is the band of nervous tissue which separates itself from the surface of the collar 
on the dorsal side yet retains a large number of cells and a thick band of fibers. This 
dorsal nervous system is connected with a longitudinal thickening on the dorsal side of 
the animal below the collar, but it is only slightly connected with the poorly developed 
sub-epithelial thickening on the dorsal side of the collar. There is very little indica- 
tion of a ventral nerve cord in the region of the collar. 
The nervous system under the epithelium of the proboscis has nerve fibers under 
it in about the same degree of thickness at all points. Local variations of thickness are 
probably due to special contractions at the time the specimen was killed. 
In all parts but the dorsal region of the collar the nervous system is intimately 
associated with surface epithelium. At the region of the collar the dorsal strand is 
made up of some cells and many longitudinal fibers. Below the collar the dorsal nerve 
band continues to be definitely marked from other parts of the epithelium and looks 
much like the nerve trunk of the starfish. The same is true in less degree of the 
smaller ventral nerve trunk which is seen below the collar. 
The nerve cells seem to be of two sorts. First those which may in part be sensory, 
bipolar cells reaching from near the surface down into the fibrous band. These cells 
usually fork at the inner surface of the fiber layer and give off minute branches as 
they pass through the fiber area. Second, multipolar cells whose bodies are located in 
the deeper layers of the nuclei with one or more branches which run into the fibrous 
area. 
The general appearance of a band of nerve fibers under the nuclear layers is a 
mass of fine branches with many cross lines and very many finer longitudinal strands 
which cannot be followed very far as individuals. The cross lines are those fibers 
which in some cases can be seen to be continuations of the cells of the epithelium. The 
fine longitudinal lines are in large part the small lateral branches of the cross fibers 
just mentioned. There is quite a dense network of fibers in all parts of the fibrous 
