Pomona College, Claremont, California 173 



of the closely applied deeper or hyponeura] nerves seem like the 

 less numerous dorsal nerve cells oi the ventral ganglia of arthro- 

 pods and annelids. It is understood by some that the epineural 

 nerves are sensory in I unction, the hyponeural motor, if this be so 

 then the statements in a number of places in literature that the ven- 

 tral cells ol certain arthropods arc sensory and the dorsal cells are 

 motor in I unction seems not without interest. 



Upon comparing- the si/e oi the ganglia ol small serpent stars 

 with those ot 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 til teen 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 ol 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 liber 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 si/e ol 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 ol the ganglia of arthropods and annelids 

 is shown in the arms of serpent stars. 



