156 ELEMENTARY ZOOLOGY 



base. These feathery feet project from the opened shell 

 when the animal i^undisturbed, and waving about in the 

 water catch small animals which serve as the barnacle's 

 food. When disturbed the barnacle withdraws its feet 

 and closes tightly its strong protecting shell. The acorn- 

 barnacles have no stalk, but look like a low bluntly- 

 pointed pyramid, this appearance being due to the 

 converging arrangement of six calcareous plates in its 

 body-wall. 



The barnacles present several unusual conditions with 

 regard to the internal organs. They have no heart nor 

 any blood-vessels ; most of the species are hermaphroditic ; 

 and there are other indications of a degenerate condition. 

 This degeneration of the barnacles is due to their fixed 

 Hfe, the results of which are like those of a parasitic life. 

 The young barnacles when hatched from the egg are free- 

 swimming larvae as with the other Crustacea. They 

 finally attach themselves and undergo the changes, some 

 of them of degenerative nature, which produce the body- 

 structure of the adult. It was long a belief among many 

 people that the barnacle produced the barnacle goose. 

 Pictures in ancient books show the young barnacle geese 

 issuing from the* opened shell of the barnacle. The early 

 naturalists believed barnacles, on account of the shell, to 

 be a kind of shell-fish or mollusc, but when their develop- 

 ment was thoroughly worked out, it became evident that 

 they belong to the Crustacea. 



