MANUAL OF NATURAL HISTORY. 301 



large, rounded, divided into two parts, the 

 anterior large and semilunar, the posterior 

 smaller, toothed at the sides, and ending in 

 a long pointed spine. 



CIBRHOPODS. 



The Cirrhopods, generally known under the names 

 of Acorn-shells and Barnacles, are marine articulated 

 animals, forming a class intermediate between the 

 Crustacea and the Mollusca. Their body is more 

 or less jointed, and is placed with the back down- 

 wards, the cirrhated feet being protruded from the 

 aperture of the shell ; the jaws resemble those of 

 Crustaceans, the head is indistinct, and, in the adult, 

 there are no distinct eyes or antennae ; the part cor- 

 responding to the abdomen of Crustaceans is fur- 

 nished with a series of lateral lobes, each bearing two 

 long, curled, many -jointed, ciliated false-feet, which in 

 the living animal are constantly in motion, being al- 

 ternately protruded and withdrawn, causing cur- 

 rents which procure food and subserve respiration. 

 Their nervous system resembles that of annulose 

 animals, and consists of a double series of ganglia ; 

 their blood is white, and they have a complete 

 double circulation ; from the circumstance of their 

 bodies being protected by shelly plates, they have 

 been confounded with the Mollusca. They are en- 

 dowed with locomotion only in the young state, 

 but when adult, are always fixed. 



