XI 



PHYLUM ARTHROPODA 



605 



viz; 



pair of jaws the first pair of maxillce (mx. v max. 1 ). Each maxilla 



exhibits a structure comparable to the fundamental type of the 



appendages of the Cray- 

 fish : a basal part or 



protopodite, consisting 



of two segments (podo- 



meres), supporting an 



internal ramus or endo- 



podite, and an external 



ramus or exopodite. If m.<? 



The former consists of \^^) mi 



two parts : an inner, \iiSm4&5r 



pointed, hard blade 



the lacinia (mi.), and 



an outer, softer, more 



elongated the galea 



(me.). The exopodite 



forms a palp, the maxil- 

 lary palp (pm.), consist- 

 ing of five podomeres. 



Behind these are the 



second maxillae, which 



are reducible to the 



same type, but which 



have their two basal 



segments (those of the 



protopodites) united to- 

 gether in the middle 



line to form two median 



sclerites, known respectively as mentum (m.) and submentum (sm.), 



so that the two appendages form a sort of lower lip called the 



labium. The endopodites taken to- 

 gether constitute what is termed 

 the ligula ; each is divided into two 

 parts like the endopodite of the 

 first maxillae. The exopodites form 

 -cerv three-jointed palps, the labial palps 

 (pi.). A soft pear-shaped median 

 process the tongue, lingua or hypo- 

 pharynx, is attached to the upper 

 side of the mentum : just behind it 

 is a median slit supported by two 

 chitinous pieces the entrance to 



FIG. 500. Periplaneta americana. |/U T^ar-Trm?- 

 Lateral view of the head and its ap- tlie pudiyux. 



pendages. cerv. one of the cervical The neck, or narrow region be- 



sclentes ; ey. eye ; gen. gena ; man. , ' n j-vxgivij. 



mandible ; max.*, first pair of max- tween the neaa proper and the 



illse ; max. 2 , second pair of maxilla; J.-L j jS 



thorax, is covered for the most part 



FIG. 499. Mouth parts of the Cockroach. Ibr. labrum; 

 m. mentum ; md. mandible ; mxi, anterior pair of maxillao ; 

 me. and mi. outer and inner divisions of the first and 

 second pair of maxillae ; mx. 2 , second maxillse ; pi. labial 

 palp ; pm. maxillary palp ; st. stipes ; sm. submentum. 

 (From Lang's Comparative Anatomy.) 



