AMKRICAN NEUROPTEKA. 119 



the fact of their generally similar and parallel behavior throughout 

 the Orthopteroidea. 



In the course of my examination of adult labia I noticed a struc- 

 ture which seems hitherto to have been overlooked, — namely, the 

 presence in certain Zygoptera of a distinct suture which, starting 

 from the base of the cleft of the ligula, runs transversely to within a 

 short distance of its border and, then turning backward, runs paral- 

 lel with the border down to the nientum, as shown for Euphcea 

 masoni in Plate VII, Fig. 6. The transverse portion of this line is 

 bordered with hairs and, at the side nearest the cleft of the ligula it 

 is produced into a point similar to that of the terminal border. In 

 Platycnemis acutipenuis (PI. VII, Fig. 6 b) we have a similar con- 

 dition, with the addition of the hairs within the suture, upon the 

 lower part of the mentum. 



The presence of this distinctly defined suture upon the mentum 

 confirmed me in the opinion which, without much supporting evi- 

 dence, is advanced by Rambur and Hagen, that the mentum is 

 formed by the consolidation of two pairs of appendages of the max- 

 illa, the lacinte and galeae, and that the lateral lobe represents the 

 palpus alone. The foregoing examination of the labia of several 

 species in embryonic stages corroborates this opinion. In the embry- 

 onic labium of Lestes uncata (PI. V, Fig 13) it will be observed that 

 the teeth in the cleft between the two halves of the developing men- 

 tum are forming in two sets, consisting of three teeth each, increas- 

 ing in size from the bottom upward and already quite strongly chiti- 

 nized. These may well be taken to represent the tip of the retarded 

 lacinise. Their sharp armature well corresponds with that of the 

 tips of this chewing part of the maxilla. The paired lobes above 

 these a short distance may well represent the tips of the retarded 

 galei:e. In the embryonic labium of Aiiax Junius (PI. IV, Fig. 2) 

 the separation between the two is marked by a deep indentation. 



This theory then assumes that the lower sets of teeth repi-esent the 

 toothed borders of the lacin?e and the upper more or less crumpled 

 lobes, the tips of the galeee, while the lateral lobe represents the j)al- 

 pus above, much modified in shape and complicated by its change in 

 function, In the development of the ligula the lacinse consolidate 

 and the lobes representing the galeae grow together above them, 

 inclosing them on all sides excepting at their juncture with the 

 mentum. This theory gains force from the fact that in many of the 



TRANS. AM. ENT. SOC. XXX. MAY. 1904. 



