igo BEES AND BEE-KEEPING. 



one taking the right, the other the left, half. 

 As they pass up and down in company with the 

 darts, they never become absolutely clear of each 

 other. Although one be at the top, and the other 

 at the bottom of the stroke, they still, in part, are 

 side by side, so that clashing or interference is im- 

 possible. Each is formed from the dart, by the 

 throwing back of two strong, parallel, chitinous, rod- 

 like pieces, supported by a truss (tr, L, Plate VII.) 

 above them. As the whole valve is necessarily 

 narrow, the space between these rods is small. 

 Above the truss we find a feathery expansion, in 

 the form of a hood, which really holds in position a 

 most delicate membrane — not represented in the 

 Figure — really a bag, mouth downwards, the edges of 

 its mouth being attached to the parallel rods, so 

 that, when the down stroke is made, the poison, with 

 which the pouch is always full, passes into, and 

 expands, the bag, as a butterfly net is opened out 

 when it sweeps through the air. Below each rod 

 depends another membrane, semicircular in outline, 

 and stiffened by numerous chitinous, branched thicken- 

 ings, seen above va. These flaps, at the down 

 stroke, separate from each other, and the better 

 drive the venom before the advancing valve. At the 

 end of the stroke, the fully-extended membranous 

 bag, by its elasticity, continues to drive on the 

 poison until its companion takes its place. At the 

 upward stroke, the bag collapses, and settles on to 

 its feathery support, which holds it in position for re- 

 filling, while the depending flaps fall together. The 

 accurate fit of the darts prevents the escape between 



