78 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8l 



first maxilla (fig. 40 B, St). The wall of the mental region, however, 

 may not be entirely or continuously chitinized (fig. 32 A), and, hence, 

 a distinction must be drawn between the entire region of the mentum, 

 and the area occupied by one or more mental sclerites. The labium 

 may contain muscles not represented in the maxillae, such as the 

 muscles associated with the orifice of the salivary duct in the grass- 

 hopper (fig. 40 D, 26, 2/), or with the silk press in the caterpillar 

 (figs. 53 C, D, 54, A, B, C, ly, 18, 19). 



The submentum corresponds functionally at least with the cardines 

 of the maxillae, since it serves to attach the labial appendage to the 

 walls of the head. The lateral articulation of its basal angles to the 



B 



Fig. 32. — Second maxillae. 



A, typical second maxillae of an insect (Periplaneta) united to form the 

 labium. B, second maxillae of a chilopod (Lithobius) united by inner angles 

 of coxae. 



ct, coxo-trochanteral joint; Cx, coxa; Gl, glossa; Mt, mentum; O, levator 

 muscle of telopodite (palpus) ; Pgl, paraglossa; Pig, pelpiger; Pip, palpus; Q, 

 depressor muscle of telopodite (palpus) ; Smt, submentum. 



margins of the cranium in orthopteroid insects (figs. 18 B, C, 36 C, /) 

 suggests, moreover, that the points of attachment are the true 

 basal articulations of the second maxillae with the cranium, corre- 

 sponding with the articulations of the cardines (e) in the first maxillae. 

 It is possible, of course, that a median part of the labial sternum has 

 been incorporated into the submentum. To accept the proposal, how- 

 ever, that the entire submentum is the sternum of the labial segment, 

 is to assume that the sternum itself has become articulated laterally 

 to the tergum of its segment, and that it alone bears the segmental 

 appendages. Such assumed relations violate the basic principles of 

 segmental inorphology, and thus throw suspicion on the evidence 

 given in their support. 



