430 



ARTHROPODA. 



velopment and become strong walking legs, terminated either with 

 claws or pincers (chelae). 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/ 



FIG. 436. Erichthus stage of Squilla (orig.). 



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

 against it. 



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

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

 maxillipeds (7, 6, 5)show clearly a biramous condition, while the maxillae 

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

 dibles (2) there is always a strong basal joint, the edge of which serves as a 

 jaw, while this may bear additional joints, the palpus. Behind the mouth 

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

 appendages. The antennae are usually distinguished from their size as 

 antennae (second pair) and antennulce (first pair, fig. 404). They have large 

 basal portions, which in the antennulae bear two many-jointed flagella, 



