INSECTA JAWS. 



523 



lobed, or crooked. In the last case the first or second joint is elon- 

 gated forming the shaft, to which the distal and shorter joints are 

 attached at an angle as the flagellum (Apis}. 



The following structures enter into the formation of the mouth 

 parts : the upper lip (labruni), the upper jaws (mandibles), the first 

 pair of maxillfe or lower jaws, the second pair of maxillae or lower 

 lip (labium). The upper lip is a plate, which is usually movably 

 articulated to the cephalic shield and covers the mouth from above. 

 Beneath the upper lip to the right and left are the mandibles or upper 

 jaws, in the form of two palpless biting plates ; they are unjointed, 

 and therefore more powerful as masticatory organs. The first pair 

 of maxillae or lower jaws have a more complicated structure. They 

 are composed of fl 



several joints, 

 and are, there- 

 fore, adapted for 

 less powerful but 

 more varied move- 

 ments in aid of 

 the masticatory 

 process. 



The maxillae of 

 the first pair (fig. 

 430) are made up 

 of the following 

 parts : a short 

 basal joint (cardo, 

 C), a longer se- 

 cond joint or 

 shaft (stipes, 8t) 

 with an external scale (squama palpigera), to which is attached 

 a many-jointed palp (palpus maxillaris, JLxt.). Two blades, an 

 internal and external, are attached to the distal end of the second 

 joint [and known respectively as lacinia and galea] (lolus externns, 

 interims, L. in, L. ex). The maxillae of the second pair arise from 

 the throat, and are partially fused together across the middle line 

 so as to form the unpaired lower lip or labium. It is rarely the case 

 that all the parts of the firt maxillae are discernible in the labium, 

 the fusion being generally accompanied by the reduction and dis- 

 appearance of certain parts. There are, however, cases in which 

 a,ll the elements of the first maxilke can be shown to exist (Ortlwp- 



Fic. 430. Mouth parts of a Bla/fa (aftor Psivi.amy). n, Head 

 seen from the front: Oc, ocelli; Mit, maxillary pnlp ; Lt, 

 labial palp, b, Upper lip (labrum, Lr). <; Mandible (Ma), 

 d, 1st maxilla : C, Cardo ; St, stipes; L. in, lolras interims; 

 L. ex, Lobus externus. e, 2nd maxilla; or labiuiu (lower 

 lip), clearly composed of two halves. 



