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NO. 3 INSECT HEAD SNODGRASS "JJ 



area supporting the palpus is frequently differentiated from the rest 

 of the stipes, and is then distinguished as the palpifer (fig. 31 A, 

 F//). When the delimiting suture of the palpifer region extends to 

 the galea, the palpifer appears to support both the galea and the 

 palpus. That the palpifer is not a segment of the appendage is shown 

 by the fact that inuscles neither arise tinthin it nor are inserted upon 

 it. The muscles that move the palpus as a whole have their origins 

 within the main part of the stipes, and always pass through the pal- 

 pifer, if the latter is present, to 1)e inserted on the ])roxinial segment 

 of the palpus (figs. 25 C, 31 A-E, 0,0). The pal])us muscles, then, 

 may be taken as identification marks of the true basal segment of the 

 palpus. Since they are typically inserted one dorsally and the other 

 ventrally, relative to the vertical axis of the appendage, they are 

 evidently a levator ( O ) and a depressor ( ) of the palpus. The 

 number of segments in the maxillary palpus varies much in different 

 insects. Machilis perhaps presents the maximum number of seven 

 (fig. 31 A) : the palpus of the roach with five segments is more typical 

 (fig. 25). Evidence will later be given indicating that the palpus is 

 the telopodite of the maxillary appendage, and that its basal articula- 

 tion with the stipes, or palpifer, is the coxo-trochanteral joint of a 

 more generalized limb (fig. 35 A, B, C, ct) . A joint near the middle 

 of the palpus (figs. 25 C, 35 A, B. ft) often suggests the femero- 

 tibial fiexvn-e. 



THE SECOND MAXILLAE 



The second maxillae of insects are unquestionably united in the 

 labium. The correspondence in external relations between the parts of 

 each half of a typical labial appendage and those of an entire maxilla 

 is so close that most entomologists have not hesitated to assume an 

 homology of the submentum (figs. 32 A, 40 D, Suit) with the cardines, 

 of the mentum {Mt) with the stipites, of the glossae {Gl) with the 

 laciniae, and of the paraglossal {Pgl) with the galeae. Some writers, 

 however, have contended that the sul)mentum, or both the submentum 

 and the mentum represent the sternum of the labial segment. Thus, 

 Crampton in a recent paper (1928) adopts the idea of Holmgren 

 ( 1909) that the submentum and mentum arc derived from the sternum 

 of the labial segment. 



In an orthopteroid labium (fig. 40 D), the muscles of the 

 palpi {28, jq), and the muscles of the terminal lobes (-^5) arise in the 

 mentum {Mt), and this relation, together with the presence of muscles 

 from the mentum to the tentorium (i-J, 24). must certainl\- identify 

 the region of the mentum in the la1)ium with that of the stipes in a 



