194 



ZOOLOGY. 



suckers, excepting those at the end of the arms, which are 

 tentacle-like. We have already described the common star- 

 fish of our north-eastern coast, Asterias Forbesii of Desor 

 (Fig. 137). This and the allied varieties are abundant on 

 mussel and oyster beds, being very injurious to the latter, 

 which serve them as food. The star-fish projects its capa- 

 cious stomach, turning it inside out. between the open 

 valves of the oyster, meanwhile pouring out a poisonous fluid 

 from the unicellular glands of the midgut so as to surround 

 the oyster with a sticky envelope, before the animal is drawn 

 out of its shell. 



Fig. 137. A star-fish, which has been placed ou its back, righting itself. After 

 Romanes. 



The bodies of star-fishes as well as sea-urchins (Echini) 

 are covered with pedicellarice, which in the former are situ- 

 ated around the base of the spines on the upper side of the 

 body. They are pincer-like, consisting of but two prongs. 

 Ju the sea-urchins they are three-pronged, and scattered ir- 

 regularly over the surface of the body. Their use is net 

 really known. Star-fish have the sense of smell.* 



The development of this species (and its ally or variety, 

 A. benjlinus) has been studied by A. Agassiz. After pass- 



* It is localized iu the suckers at the back of the eye-plate (Prulmi. 



