59 



diagrammatic labium of a cockroach confirms this (PI. VII., fig. E) ; 

 for a very primitive (I think I may say most primitive) form of 

 labium occurs in the Orthoptera and Isoptera. This we may com- 

 pare with the labium (also diagrammatic) of one of the large 

 dragonflies (PI. VII., fig. A, //;/). Although it is quite agreed that in 

 the first maxillae the inner lobe is caused by the fusion of the galea 

 and lacinia, in the case of the second maxillae this was once 

 questioned ; but the same view seems to be accepted now. Rambur 

 and Hagen, advanced the opinion that the lateral lobe represents 

 the palpus only, while the central part was the result of the fusion 

 of galeae and laciniae. Gerstaecker, however, thought that the 

 lateral lobe was made up of palpus and galea. Apart from the fact 

 that non-parallel variation is scarcely to be expected in this case, 

 there are various little indications, especially in the naiad stage and 

 in imaginal Zygoptera, which tend to support the opinion of Rambur 

 and Hagen. PI. VII.,fig. A, ^fc/, will serve to illustrate all the imaginal 

 labia, if mention is made of one or two points of variation in the 

 sub-families. 



All the families and sub-families with British representatives, are 

 shewn in the following table. 



Although there is some amount of variation in the i in a t/iua I labium, 

 yet in all cases the principal parts are easily recognisable — broad 

 base, projecting median lobe ( = ligula), squames supporting lateral 

 lobes, moveable hook, and end hook. Some variations are : — In the 

 Zygoptera and the old Anisoptera the ligula is prominent and 



