HARD PARTS OF THE GRASSHOPPER. 245 



backwards, to articulate with the lower anterior edge of 

 the gena, by a joint which allows them to move towards 

 and away from the median line, but in no other direction. 



L On the nearly flat posterior aspect of the head 

 notice : 



(i.) The large occipital foramen, by which the cavity 

 of the head communicates with that of the neck. This 

 foramen is bounded above by the epicranium ; at the sides 

 by the gena, and below by a crescent-shaped sternal ele- 

 ment, the gula (Fig. 131, D, gu). 



(ii.) Movably articulated with the lower straight edge 

 of the gula (Fig. 131, D, gu) is the labium or lower lip 

 (Fig. 131, D), formed by the union of a pair of append- 

 ages, which are immovably united, but exhibit, upon the 

 median line, traces of this union. The labium consists 

 of: 



(a.) A basal portion, the mentum (Fig. 131, D, m). 



(b.) A pair of terminal apron-shaped pieces, convex 

 behind and concave in front, the two halves of the ligula 

 (Fig. 131, Z), Iff). 



(c.) On each outer edge of the mentum is a small piece, 

 thepalpiger (Fig. 131, D,pg). 



(d.} Upon this is the three-jointed labial palpus (Fig. 

 131, D, n). 



(e.) Between the base of the mentum and the gula is a 

 small immovable piece, the submentum (sm). 



m. Draw the posterior aspect of the head and labium. 



n. Remove the gula and the labium, and expose the 

 posterior faces of the anterior mouth parts. 



(i.) Notice, in the median line, a dark-colored, chitinous, 

 spiny pad, the metastorna or tongue (Fig. 131, E), which 

 forms the posterior boundary of the mouth. Pull it out 

 with the forceps, and note the rows of spines which cover 

 its anterior face. 



