STAEFISH 91 



are discharged directly into the water. Here development takes 

 place resulting in the formation of minute larvae in no manner 

 resembling the adult .starfish. The adult form is reached only 

 through a complicated metamorphosis of the free-swimming 

 larval stage. 



Nervous System 



Pull oE 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 circum-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 

 inconspicuous in preserved specimens. 



4. 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 it walls? Connection of its 

 lower end with the ri7ig canal? 



2. Amhulacral or tube feet. Position? 



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

 rows ? Are they connected with tube feet ? 



4. Badial canals or ivatcr tnhcs. One on the aboral side 

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

 radial nerve. 



5. Make out the connections between the different parts of 

 the water vascular sj^stem. 



6. Can you think of possible uses for it ? State j^our views 



