1916 Pomona College of Entomology and Zoology, Vol. VIII, No. 4, Deci mber 



The Central Nervous System of Serpent 



Stars 



WILLIAM A. HILTON 



Several summers ago the activities of small serpent stars attracted 

 my attention. The young of Ophioderma panamensis Lutken, pos- 

 sibly mingled with the minute young of Ophionereis annulata Le 

 Conte were found in great numbers at Laguna Beach. These little 

 creatures seemed fully as active as the adults. As compared to 

 mature forms they were often very minute, the diameter of the discs 

 being one-tenth or one-twentieth that of the adults. 



As compared with the starfish the adult nervous system is, of 

 course, more highly organized although as well known it follows 

 the same general plan of arrangement. Tn the adult form studied, 

 Ophioderma, the larger more superficial or epineural nerve bands 

 were best marked and were chiefly studied. The hyponeural nerves 

 were not prominent or well separated from the epineural. The 

 large pedal ganglia are well marked and of the same general struc- 

 ture as the radial parts of the epineural strands, but the cells seemed 

 a little larger and the fibers not quite so marked in the same prepara- 

 tion. 



In some quite small serpent stars where the radial and circumoral 

 systems were compared although the structure was the same in 

 general, the more central part of the nervous system was much 

 larger. In a specimen with a disc one milimeter in diameter the 

 radial was about half the diameter of the circumoral. This would 

 indicate more of a centralization than in the starfish. 



A section across the radial nerve shows the nerve cells similar 

 to those in starfish, located in the outer zone, two or three cells deep. 

 The wider fiber area is quite homogeneous in some preparations but 

 in others there were here found large numbers of cell processes 

 similar to those of starfish. Certain rather fortunate slides showed 

 these processes with great clearness. The best results of this sort 

 were obtained from specimens fixed in Flemming's fluid, the cal- 

 cium salts of the skeleton were afterward removed by means of acid 



