ARTHROPODS. CLASS CRUSTACEA 97 
is open along one side, and allows the feather-like feet to 
project and produce currents in the surrounding water 
which brings food within reach. In the acorn-barnacles 
(Fig. 55) the stalk is absent, and the body, though possess- 
Fig. 55.—Barnacles. Acorn-barnacles chiefly in lower part of figure ; goose-barnacles 
above. Natural size. 
ing the same general character as the goose-barnacles, is 
shorter, and enclosed in a strong palisade consisting of six 
calcareous plates. 
The larger number of barnacles attach themselves to 
the supports of wharves, the hulls of ships, floating tim- 
bers, the rocks from the shore-line down to considerable 
depth, and a few species occur on the skin of sharks and 
whales. On the other hand, there are several species which 
are parasitic, and in accordance with this mode of life ex- 
hibit various degrees of degeneration. In the most extreme 
