CLASS ASTEROIDEA. 19 







arm, is a longitudinal groove from which project a multi- 

 tude of small retractile tentacles, the ambulacral uppend- 

 ages. Other species of Crinoids finally break from the 

 top of the stock and crawl away, free forms. These free 

 Crinoids introduce us to the Star-fishes. 



CLASS ASTEROIDEA (as ter oid'e a). 



The STAR-FISHES have the body much flattened and 

 the ambulacral appendages, when present, provided with 

 terminal suckers, of use in locomotion as well as in secur- 

 ing food. All are invariably free, i. e., are not supported 

 by a stock. 



ORDER ASTERIDEA (as ter id'e a). 



The common Star-fish is abundant along the sea-shore, 

 where it commits great depredations on the oyster beds. 

 Upon the lower side of each ray are several rows of am- 

 bulacral suckers, which may be thrust forth and become 

 attached to foreign bodies; they are then contracted and 

 the animal drawn up to the point of attachment, thus 

 producing a slow locomotion. As the animal crawls, 

 mouth downward, these suckers bring it over its food, 

 which is thrust through the mouth into the stomach ; or 

 if the morsels are large, the stomach is everted, and the 

 food digested outside the animal, the stomach being 

 finally drawn back into the body. At the tip of each 

 ray is a small red spot, the eye, which may give the 

 animal the perception of light and shade. A small nerve 

 can be traced from this spot, along the lower side of the 

 arm to a nervous ring surrounding the mouth.* Recent. 



* As each arm contains special branches of all the necessary organs, the 

 Star-fish can endure severe mutilation. Lost arms are replaced, and even single 

 arms will live and finally develop into complete Stars. All the Star-fishes, of 



