Bees are able to walk freely in an inverted position, either on glass or other slippery substances. The peculiar mechanism of their feet, which enables them to do so, consists in their having in the middle of each hook a thin membranous little cup or sucker that is alternately exhausted and filled with air. Flies have the same beautiful apparatus--hence a fly commonly selects the ceiling for a resting-place. These little air-cups, or exhausted receivers, may be seen by applying a strong magnifying-glass to a window that has a bee traversing the reverse side. The edges of these little suckers are serrated, so as to close against any kind of surface to which their legs may be applied. This apparatus may be also serviceable for gathering the pollen before transmitting it to the baskets on the hind legs. Besides these appendages and apparatus of the thorax, that region is traversed by the œsophagus or gullet (the opening to which will be found in Plate I, fig. 2 _c_), on its way to the digestive and other organs, situate in the third part of the insect--viz., the abdomen. The covering of the thorax, with the external covering of the gullet, may be seen in the drawing of the magnified dissected body of the bee (Plate II., fig. 1). The breathing apparatus of bees is a very remarkable feature: they have no lungs, but, instead, air-vessels or tubes, ramifying through every part of the frame. These openings, called "spiracles," are found in the sides of their bodies, behind the wings. Two of the openings are located in the thorax, and one on each side of the scales of the abdomen.