XI 



PHYLUM ARTHROPODA 



573 



and 455, man.}, 



JJIX. 



a pair of stout mandibles (Fig. 

 which work horizon- 



lly like those of the 

 yfish ; their inner 



ges are divided 

 into a number of 

 teeth. Behind the 

 mandibles are a more 

 flexible pair of jaws 

 the first pair of 

 maxillce (mx. 1 , max. 1 ). 

 Each maxilla exhibits 

 a structure compar- 

 able to the funda- 

 mental type of the 

 appendages of the 

 Crayfish ; a basal part 

 W protopodite, consist- 

 ing of two segments 

 (podomeres), support- 

 ing an internal ramus 

 or endopodite, and an 

 external ramus or 

 exopodite. The former 

 consists of two parts : 

 an inner, pointed, hard 

 blade the lacinia 

 (mi.), and an outer, 

 softer, more elongated the galea (me.). The exopodite forms a 

 palp, the maxillary palp (pm.), consisting of five podomeres. Behind 



these are the second maxillae, which 



y are reducible to the same type, but 



/Cf^v'^ which have their two basal seg- 



i ti iK. ments (those of the protopodites) 



united together in the middle line, 

 to form two median sclerites, 

 known respectively as mentum (m.) 

 and sitbmentt(,m(sm.), so that the two 

 appendages form a sort of lower lip 

 called the labium. The endopo- 

 rlites taken together constitute 

 what is termed the ligula ; each 

 is divided into two parts like the 

 endopodite of the first maxillae. 

 The exopodites form three-jointed 



palps, the labial milvS (-pi.). 

 mi i 



I he neck, or narrow region 



FIG. 454. Mouth parts of the Cockroach ; Ibr. labrum ; 

 md. mandible ; mx l . anterior pair of maxillse ; m. mentum ; 

 me. and mi,, outer and inner divisions of the second 

 pair of maxillae; pi. labrel palp. ; pm. maxillary palp; 

 st. stipes ; sm. submentum. .(From Lang's Comparative 

 Anatomy.') 



;' .r'eye gena 



mandible ; max*., first pair of max- 

 -,,uu'-. second pair of maxillae 



