INSECTS: THEIR FEET 137 



In the foot of the fly under our own observation you 

 may see how well the joints of the tarsus are covered with 

 hairs, or rather stiff pointed spines, of various dimensions 

 and distances apart, and hence how suitable these are for 

 acting the part of combs to cleanse the palms. But these 

 last are the organs that most claim and deserve our ex- 

 amination. In the specimen of the little Musca that I have 

 imprisoned, the last tarsal joint is terminated by two strong 

 divergent hooks which are themselves well clothed with 

 spines, and by two membranous flaps or palms beneath 

 them. These are nearly oval in outline, though in some 

 species they are nearly square, or 

 triangular, and in some of a very 

 irregular shape. They are thin, 

 membranous, and transparent, and 

 when a strong light is reflected 

 through them by means of the 

 achromatic condenser, we see their 

 structure under this power of 600 

 diameters very distinctly. 



The inferior surface of the 

 palm, on which we are now look- 

 ing, is divided into a vast num- 

 ber of lozenge-shaped areas, which 

 appear to be scales overlapping 

 each other, or they may be di- 

 vided merely by depressed lines. From the centre of each 

 area proceeds a very slender, soft, and flexible pellucid 

 filament, which reaches downward to the surface on which 

 the fly is walking, and is there slightly hooked and en- 

 larged into a minute fleshy bulb. Those from the areas 

 near and at the margins of the palms more and more arch 



FOOT OF FLY. 



