VJ16 Pomona Joiiriidl of Kntoinolocjy and Zoology , I'ol. I'lII , No. 3 , Scptc/nbcr 



Some Remarks on the Central Nervous 

 System of the Starfish 



WILLIAM A. HILTON 



There are several questions in connection with the central nervous 

 system of star fish which, so far as T know, are not answered by 

 older or more recent in\-estigations. They are as follows: 



1. Is there any special center in the radial or circum-oral ner\'ous 



system? 



2. If there are true nerve cells how are they related? 



3. Are there true neurolihrillae? 



4. Is there any tigroid substance? 



5. Is there any connection between the superficial and the deep 



radial systems? 



6. Are all the elements in the central nervous system nerve cells? 



7. Do different species differ from each other materially? 



Six species of starfish were collected at Laguna Beach. Two 

 methods were used for fixation; hot mercuric cloride or Flemming's 

 fluid were used upon the whole animal. The first reagent was 

 especially useful in extending the animals and whitening the radial 

 and circum-oral nerves. Borax carmine was used with good results 

 in staining after the first fixation and iron hematoxylin after the 

 second. By both methods cells and fibers were clearly shown. 



In all the specimens examined just after killing, the central por- 

 tion of the radial or circum-oral ner\'es seemed like a definite line 

 of nervous tissue. Sections showed in some cases a thicker epithel- 

 ium in the mid-ventral line of the nerves. The radial nerve was 

 often less thick than the central part of the nerve ring. The chief 

 structural difference between the radial and circum-oral nerves in 

 their central portions was in the arrangement of the cells and fibers. 

 In these regions the nerve fibers seem to cross more and run in 

 towards the middle line. This was very marked in some specimens. 

 Some indication of this is given by Cuenot, 1890. 



In the central nervous system there are unipolar and bipolar cells 

 with long slender processes reaching through the whole thickness of 



