CHAPTER V 



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ECHINODERMS (SPINY ANIMALS) 



The Starfish 



FIG. 52. — Starfish on a rocky shore. 



Suggestions. Since the echinoderms are aberrant though inter- 

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



chapter may be 

 .».«£SG!fct 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 

 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 

 instructive. 



External Features. — 



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 

 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 



34 



PLAN of starfish ; III, madreporite. 



