90 EVENINGS AT THE MICROSCOPE 



and are, during life, filled with a subtile fluid, which is 

 supplied from the vessels of the body. They contain also 

 ramifications of the exquisite spiral air-vessels, which we 

 shall presently consider, so that both air and blood circu- 

 late in them. 



In this wing of the Bee all of these structures may be 

 seen to greater advantage. The membrane appears per- 

 fectly homogeneous by transmitted light, even with so 

 high a magnifying power as 600 diameters, at least on a 

 cursory examination; though, by careful manipulation, we 

 may discern faint traces of angular lines which divide the 

 whole surface into irregular areas. But by using reflected 

 light at an oblique angle, this areolation, which indicates 

 the primary cells of the structure, is much plainer, and 

 each area is perceived to carry a single hair in its centre. 

 The hairs themselves here take the character of curved 

 spines, not unlike those of a rose tree. Along the front 

 edge of the wing they are straight, stout, densely crowded, 

 and overlapping in an inclined position; but the most in- 



teresting modification of these 

 organs is seen at the front 

 edge of the posterior pair. 

 Unlike the Fly, which has 

 but a single pair of wings, the 

 Bee has two pairs, of which 

 the fore pair is the larger and 

 more horny, the hinder pair 

 DOUBLING AND HOOKS IN A BEE'S WING, seeming to be, as it were, 

 cut out of the hinder and inner side of the fore ones. 

 The two edges the hinder edge of the fore pair and 

 the front edge of the hind pair then correspond, but 

 it is necessary that, during flight, when the wings are 



