NO. 2 



HONEY BEE — SNODGRASS 



55 



paratus in the bees is a highly interesting example of the evolution of 

 a special mechanism from a structure having originally a quite 

 different function. 



Fig. 20. — Evolution of the axillary lever. 



A, Apis mellifera L., drone, right stalk of second phragma, mesal view, 

 show^ing axillary lever (axlv) and associated fourth axillary of wing base. 

 B, same, left axillary lever, lateral view. C, Spheciiis spcciosiis (Drury), right 

 stalk of second phragma with mesal process {t) corresponding with axillary 

 lever of Apis. D, Vespula maculata (L.), same parts as in Sphecius (C). 

 E, Megarhyssa lunator (F.), right stalk of phragma with simple muscle process, 

 mesal view. F, Sirc.r abbottii Kirby, second phragma and lateral muscle lobes 

 (0, anterior (ventral) view. G, Pteronidea rihcsii (Scop.), mesothorax and 

 second phragma, lateral view, showing muscle lobe (0 with muscle from f ureal 

 arm {SA2). H, Cimbex amcricana Leach, posterior end of mesonotum with 

 second phragma, showing lateral muscle processes {t) connected by short 

 muscles {78) with arms of mesosternal furca. 



h, supporting sclerite of subalare ; o, articular process of axillary lever ; 

 s, exposed head of axillary lever associated with fourth axillary sclerite ; 

 t, muscle-bearing process of second phragma of non-apoid Hymenoptera corre- 

 sponding with axillary lever (axlv) of Apoidea. 



The large, transversely elongate median plate in the base of the 

 fore wing (fig. 19 E, m) lies close behind the humeral complex 

 (A, D), and forms a link between the first and second axillaries at 

 its mesal end, and the enlarged base of the fourth wing vein at its 



