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 Forbesit 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. 187.—A star-fish, which has been placed on its back, righting itself.—After 
Romanes. 
The bodies of star-fishes as well as sea-urchins (Echini) 
are covered with pedicellarie, 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. 
Jn the sea-urchins they are three-pronged, and scattered ir- 
regularly over the surface of the body. Their use is act 
really known. Star-fish have the sense of smell.* 
The development of this species (and its ally or variety, 
A. berylinus) has been studied by A. Agassiz. After pass- 
* Tt is localized in the suckers at the back of the eye-plate (Pruho). 
