The Central Nervous System of a Long- 

 Armed Serpent Star 



WILLIAM A. HILTON 



The specimens were found in the sand of Balboa Bay. A specimen was deter- 

 mined by Dr. Clark as probably Amphiodia barbara Lyman. When obtained these 

 creatures move their arms very vigorously. When in the sand they bury themselves 

 very effectively. Out of the sand the arms are not moved to so good purpose, and 

 they become tangled. 



The great length of the arms and the smallness of the disc made these interesting 

 objects for study. Sections were made of the arms close to the disc and at their tips. 

 In the specimen from which the sketches were made, the arm sectioned was 250 mm 

 long and the disc 10 mm in diameter. The arms do not taper much and the radial 

 nerve is about the same size for some distance. At about one centimeter from the 

 tip of the arm the diameter of the nerve trunk is much less to correspond to the 

 smaller diameter of the arm. At the very tip of the arm the nerve cord is of course 

 very much reduced, but it is larger in proportion than it was at other parts of the 

 arm. (Contribution from the Zoological Department of Pomona College.) 



Fig. 1. Cross section of the radial nerve of Amphiodia, section taken near the 

 disc. X3 50. Aboral side up. 



Fig. 2. Section across the radial nerve near the tip of the arm. Aboral side up. 



X350. 



Fig. 3. and Fig. 4. Sections across the arm at the base and at the tip, showing the 

 outline of the arm with the nerve trunk within. Aboral side up. X70. 



