BARNACLES. 



533 



Fifj. 6. — Acorn Barnacle 



(^Btilaiuis halanoides). 



Nat. size. 



Order IV. — Cireipedia. 

 By recent authors the Cirripedia have been treated as a section of the Crustacea, 

 from which, however, they differ so much when adult, that they were formerly 

 regarded as a separate class. In their perfect state they are fixed immov- 

 ably by their heads to a rock, or some other object submerged in the sea, and 

 are without antennae, eyes, or any means of loco- 

 motion. Their bodies are enclosed more or less 

 completely in a calcareous shell, formed of several 

 parts, which led to the earlier naturalists regarding 

 them as MoUusca, and their shells were called Mul- 

 tivalves by collectors, in opposition to Univalves and 

 Bivalves. In the larval stages they are provided 

 with antennte, eyes, and swimming-feet, the last of 

 which become modified into short, jointed, cirrhated 

 appendages, of which there are usually six pairs, 

 and which are used to capture prey. They are 

 generally hermophrodite. All the species are marine. A peculiar interest 

 attaches to these animals, owing to their having formed a special object 

 of study with Charles Darwin, who published an elaborate 

 monograph upon them in 1851 and 1854. There are several 

 sub-divisions of the Cirripedia, many of which live para- 

 sitically on various Crustacea, MoUusca, or on other Cirripedia. 

 The only two families which we shall notice here are the 

 Baianidce and the Lepadidu;. 



The Balaiildce or acorn barnacles attach themselves to 

 the rocks, often between tide-marks, after the manner of a 

 limpet ; but they can always be distin- 

 guished from true MoUusca by their multi- Acorn Barnacles 

 valve shells. The Lepaitidce, on the other (Ualanida;). 

 hand, fix themselves by a fleshy stalk to any 

 suitable object, from which they hang. Some of the larger 

 marine animals are often chosen by them ; and they fre- 

 quently attach themselves in great numbers 

 to the bottoms of wooden ships, which re- Goose Barnacles 

 quire to be periodically freed from such (Lepadidie). 

 appendages. There was a curious belief in 

 the Middle Ages that the bird known as the barnacle 

 goose was born from hanging barnacles, and a common 

 barnacle was named Lepas aiiatifera by Linnjeus on this 

 account. Old traditions of this description, when investi- 

 withoufc prejudice, almost always prove to contain some germ of 

 truth ; but it is difficult to imagine in what curious error the story of the 

 barnacle goose could have originated. 



i'ig. 7.— Goose 



Baunacle 



{Lepas anati- 



fera). J Nat. size. 



SUB-CLASS II.— MALACOSTRACA. 



The Malacostraca, which include all the higher Crustacea, are normally 

 composed of 20 segments ; 13 segments, each bearing a pair of jointed ap- 



