40 PREDACIOUS AND PARASITIC 



seen from above, the nearest approach to the Coleoptera may be 

 discerned, the organ consisting apparently of a single lobe of 

 slight thickness and covered with short hairs. It is without any 

 external indication of division, and in the drawing is shown partly 

 hidden beneath an extensive organ, which appears to represent the 

 true ligula. Possibly, it is this which has led naturalists to recog- 

 nise a resemblance to the general structure of similar parts in the 

 Orthoptera. 



In the labium of Hemerobius, which is shown at Fig. i on the 

 same plate, we have a far more normal structure. Here the 

 central lobe, which appears to be without any trace of division, is 

 flanked on either side by a smaller lobe, the divisions being very 

 clearly cut down to nearly the centre of the organ. It is also 

 pretty evident, on careful examination, that some kind of bi-lateral 

 structure exists in the central lobe, though, as I have said, there is 

 no sign of division externally. It resembles the same organ in 

 Sialis in its short, stout hairs and in the presence of a superior 

 lobe, which must be assumed to be the homologue of the ligula of 

 the Diptera. Here, then, in one of the most typical families of 

 the Plannipentiia, we have a labium, deeply divided, and of a form 

 widely differing from that of the typical Coleoptera. Indeed, I have 

 been more than once inclined to suspect the existence of obsolete 

 or partly atrophied structure resembling the pseudo tracheae of 

 the Diptera. 



In Fig. 3 it will be seen that the labium of Agrion partakes 

 even less of the structure of the Orthoptera than that of Heviero- 

 bius does of the Coleopterous formation. In it the middle division 

 scarcely extends beyond a notch on the frontal edge, and although 

 the form and arrangement of the hairs suggest the labium of the 

 former order rather than that of a beetle, yet the general structure 

 is so utterly at variance with that prevailing among the Orthoptera 

 that it will scarcely be necessary to pursue the comparison further. 



In Libellula (Fig. 4) we find an organ which, under some cir- 

 cumstances, may be thought to present a definite resemblance to 

 the Orthoptera in regard to the central division. But a careful 

 examination of the exterior (ventral) surface, in a natural condition, 

 reveals no more than an axial depression, which it is difficult to 

 believe can represent a true division into lobes ; and an examina- 



