CHAPTER V 



ECHINODERMS (SPINY ANIMALS) 



THE STARFISH 



SUGGESTIONS. Since the echinoderms are aberrant though inter- 

 esting forms not in the regular line of development of animals, this 



chapter may be 

 omitted if it 

 is desired to 

 shorten the 

 course. The 

 common star- 

 fish occurs 

 along the At- 

 lantic coast. It 

 is captured by 

 wading along 

 FIG. 52. Starfish on a rocky shore. the shore when 



the tide is. out. 



It is killed by immersion in warm, fresh water. Specimens are usually 

 preserved in 4 per cent formalin. Dried starfish and sea urchins are also 

 useful. A living starfish kept 

 in a pail of salt water will be x 



instructive. 



External Features. 5 



Starfish are usually brown 

 or yellow. Why? (See 

 Fig. 52.) Has it a head or 

 tail ? Right and left sides ? 

 What is the shape of the 



,. 7 . . , , FIG. 53. PLAN of starfish ; III, madreporite. 



disk, or part which bears 



the five arms or rays ? (Fig. 53.) Does the body as a whole 

 have symmetry on two sides of a line (bilateral symmetry), or 

 around a point (radial symmetry) ? Do the separate rays have 



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