STARFISH 83 



NERVOUS SYSTEM 



Pull off all the tube feet and interambulacral spines from 

 one ray and note : 



1. The radial nerves, one at the bottom of each ambulacral 

 groove. Trace it down to the peristome and find its connection 

 with 



2. The drum-oral nerve ring. 



3. Each radial nerve ends at the tip of the ray in an eye 

 spot which is brightly colored in living animals but usually in- 

 conspicuous in preserved specimens. 



Make a diagram of the nervous system. 



WATER VASCULAR SYSTEM 



1. The stone canal extends down from the sieve or madre- 

 poric plate. Shape? Nature of its walls? Connection of its 

 lower end with the circum-oral canal? 



2. Ambulacral or tube feet. Position? 



3. Ampullae. Occur inside the body cavity. Number of 

 rows? Are they connected with tube feet? 



4. Radial canals or water tubes. One on the aboral side 

 of each radial nerve band. Expose one by scraping away a radial 

 nerve. 



Make out the connections between the different parts of the 

 water vascular system. Draw the water vascular system of the 

 disc and one ray. Can you think of possible uses for it? State 

 your views and have them criticized before incorporating them 

 in your notes. How does the animal crawl? Notes required. 



REFERENCES 



Jennings, H. S., 1907. Behavior of the Starfish Asterias forreri. 

 Uni. Calif. Publ. Zool. 4. 



Mead, A. D., 1900. The Natural History of the Starfish. 

 Bull, U. S. Fish Comm. for 1899, 203-244. 



