430 



ARTHROPODA. 



velopmoiit and become strong walking legs, terminated either with 

 claws or jiincers (cliel^). Usually the first pair is distinguished 

 from the others by its size and by being chelate, and becomes not 

 locomotor but grasping in function. In the development of a 

 chela the penult joint sends out a strong process, the 'thumb," 



Fro. 436.— Erichtlius stage of SquiUn (orig.). 



which extends as far as the last joint (the ■ finger '), which closes 



against it. 



The mouth parts — a pair of mandibles, two pairs of maxillfe, and three 

 pairs of maxillipeds (fig. 404)— lie in front of the first pair of legs. The 

 maxillipeds (7, 6, 5)sliow clearly a biramous condition, while the maxilla? 

 (4, 3) retain considerable of the original phyllopod character. In the man- 

 dibles (3) there is always a strong basal joint, the edge of which serves as a 

 jaw, while this may bear additional joints, \he pappus. Behind the month 

 are a pair of scales, the paragnaths or mefastoma, formerly regarded as 

 appendages. The antennfe are usually distinguished from their size as 

 antennae (second pair) and antenniilie (first paii-, flg. 404). They have larfe 

 Ijasal portions, which in the anteunuhe bear two many-jointed flagella, 



