CHAPTER V 



FIG. 52. Starfish on a rocky shore. 



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 

 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 N 



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 FlG - 53- - PLAN of starfish ; III. madreporite. 



the five arms or rays t (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 



