CHAPTER V 



ECHINODERMS (SPINY ANIMALS) 



THE STARFISH 

 SUGGESTIONS. Since the echinoderms are aberrant though inter- 



o 



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 



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 



4' 

 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 



34 



