IS 



THE IMAGO 



[OH. 



two lateral pieces or lobes. The broad base is considered to be 

 formed by the fusion of the sub-mentum (sm) and mentum (m). 

 Fused with the mentum distally is the projecting median lobe (ml), 

 probably representing the ligula of other mandibulate insects. 

 The form of this lobe varies greatly. In the Zygoptera and the 

 older Anisoptera it is very prominent and definitely bifid (fig. 6 A). 

 In the Aeschninae (fig. 5) the median cleft has disappeared, but 



..mh 



Fig. 6. A. Labium of Synlestes weyersi Selys ( x 25). B. Labium of Diplacodex 

 haematodes Burm. ( x 15). cl cleft of median lobe; other refeiences as in 

 fig. 5. Original. 



a slight median groove or line marks the place of its disappearance. 

 In addition, one or two hard black tubercles may project on either 

 side of this median groove. In the Libellulidae (fig. 6 B) the median 

 lobe is reduced to a small triangular piece, over which the huge 

 lateral lobes fold so as to meet one another in a long median line. 

 On either side of the mentum, the base is widened by the 

 development of two side-pieces or squames (sq) which support the 



