THE CIRRHOPODA. 289 
times of more, sometimes of less; hence many of the cirrhopods 
bear an external resemblance to the ship-barnacle. 
A very common member of this family, the Acorn-shell, is 
THE CORONULA OF THE WHALE, 
(Coronula diadema.) 
frequently found covering the rocks of the shore left dry by the 
retreating tide. Their scientific name is Balanus balanoides. The 
acorn-shells are not particular as to where they locate their colony. 
They are as frequently found fixed to the shells of living mollusks 
THE TUBICINELLA OF THE WHALE. 
(Tubicinella balenarum.) 
as to the rocks. It is interesting to watch the acorn-shells, which 
look so uninteresting when grouped upon a dry rock, when they 
are covered by the water. They may often be found in a little 
pool upon the beach. The sharp-edged shells gape open, and 
out come the delicate cirrhi, which, exactly as a fisherman would 
throw a casting-net, the balanus flings out into the water, and 
draws back again, capturing all the little animalcule within its 
sweep. Some cirrhopods are found as parasites on those hulks 
