Pomona College, Claremont, California 173 
of the closely applied deeper or hyponeural nerves seem like the 
less numerous dorsal nerve cells of the ventral ganglia of arthro- 
pods and annelids. It is understood by some that the epineural 
nerves are sensory in function, the hyponeural motor, if this be so 
then the statements in a number of places in literature that the ven- 
tral cells of certain arthropods are sensory and the dorsal cells are 
motor in function seems not without interest. 
Upon comparing the size of the ganglia of small serpent stars 
with those of adults, it was found that the nervous system is in pro- 
portion, much better developed in the small specimens. All the 
larger figures shown were drawn to the same scale, yet the figures of 
the adult were from a specimen with a disc fifteen times that of the 
small specimens. The radial nerve of the small specimen shown 
in cross section is through its narrowest part. In a small specimen 
of 1 mm. disc diameter the radial nerve was one-third of the diam- 
eter of the arm. In an adult but small specimen the arm was 3.5 
mm. in diameter while the nerve strand was only .04 to .01 mm. 
in diameter. The nerve cells were slightly more numerous in cell 
areas in the small specimens than in the large. 
SOME POINTS SUGGESTED BY THESE OBSERVATIONS 
1. The synapse in this form and probably other echinoderms 
seems to be by simple contact, possibly at the sides as well as at the 
terminals of nerve cells. 
2. If fibrils are found within nerve cells they are represented by 
very few, possibly only one to a fiber in many cases. 
3. Some slight indications of tigroid substance were found. 
4. With the growth of the nervous system the nerve cells become 
less abundant at any one place while the relative size of the nerves 
becomes much less in the adult. 
5. The nervous system of the serpent stars looks much more 
like the nervous structures of more complex forms than does that 
of the starfish. 
6. A striking general resemblance of the nervous system to the 
segmental arrangement of the ganglia of arthropods and annelids 
is shown in the arms of serpent stars. 
