INVERTEBRATE ANIMALS. 61 



several pieces and open at the top when not closed 

 by the pyramidal operculum. To the thorax are attached 

 six pairs of forked limbs bearing twenty-four plumes 

 or cirri. Rocks and stones near low-water mark for 

 miles together on various parts of the British coasts 

 are thickly coated with Balanus crenatus ; other spe- 

 cies are found attached to Cetacea, Turtles, shells, and 

 corals. Balanus psittacus attains a height of eight 

 inches, and is much prized as an article of food in Chili. 

 Estimated number of species : recent, 100 (Darwin) ; 

 British, 16. 



Group 160. — Family LEPADID^. AsTraj, the Limpet. 

 Stalked Cirripedes, or Barnacles. The antennae of the 

 free larva are prehensile. Having attached itself to some 

 solid object, as a piece of timber or the bottom of a ship, 

 the anterior extremity of the animal becomes enor- 

 mously elongated forming a stalk or peduncle bearing 

 a " capitulum," constructed of calcareous plates united 

 by a membrane. Delicate plumes made up of twenty- 

 four cirri are incessantly protruded and retracted and 

 by their action currents of water are made to enter the 

 capitulum bringing food to the animal. The plates of 

 the capitulum are extensively used in the construction 

 of artificial flowers. 



The remainder of the Sub-class includes two 

 interesting but minute species, constituting the orders 

 Abdominalia and Apoda. Estimated number of spe- 

 cies : recent, 45 (Darwin) ; British, 11. 



Sessile Cirripedes are first met with in Eocene 

 deposits ; and Stalked Cirripedes have been found as 

 early as the lower Oolite ; but neither appear in any age 

 to have abounded so greatly as at the present time. 



