CHAPTER XX 



THE STARFISH AND SOME ALLIES: ECHINODERMA 



Let the mere star-fish in his vault 



Crawl in a wash of weed, indeed, 

 Rose- jacy nth to the finger-tips. 



Robert Browning 



The Starfishes 



Habitat and Distribution. The purple starfish (Aste'rias 

 vulga'ris, Fig. 120) is found most abundantly north of Cape 

 Cod in tide-pools on rocky shores, and in deep water near 

 the shore. It is only in the warmer season, however, that one 

 may witness a scene like that portrayed in the illustration. 



In addition to the species here mentioned there are several 

 other species on the Atlantic coast. The Pacific coast is 

 also well supplied with starfishes, some of which are con- 

 siderably more than a foot in diameter. While most of the 

 starfishes have only five arms, as pictured in Fig. 120, some 

 have as many as twenty arms. When the winter storms 

 come on, starfishes and many other tide-pool animals that 

 are not fixed permanently migrate to the deeper water, in 

 order to be in more protected places. 



External Structure. Up to this chapter we have been giv- 

 ing our attention to animals that have a perfect, or slightly 

 modified, bilateral symmetry. The starfish evidently has a 

 plan of structure for which we must find some other name. 



Instead of organs and structures being paired on the two 

 sides of the body they are repeated around a central axis 

 like the spokes of a wheel. In a specimen we observe five 

 arms extending from a central region. The position of the 



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