INSECTS : THEm FEET. 131 



and it is so far in favour of Mr. BlackwaU's hypothesis, 

 on which one might conjecture that from some cause 

 (perhaps of disease) the hairs of the pulvilli had poured 

 out a greater quantity of this viscid material than usual, 

 and more than the muscular strength of the fly was 

 able to cope with."* 



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 tl.e 

 palms. But tliese last are the organs that most claim 

 and deserve our examination. 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 arc 

 now looking, is divided into a vast number of lozenge- 

 shaped areas, which appear to be scales overlapping 

 each other, or they may be divided merely bj depressed 

 lines. From the centre of each area proceeds a very 

 slender, soft, and flexible pellucid filament, which 

 reaches downwards to the surface on which tlie fly is 

 walking, and is there slightly hooked and enlarged into 



* Intr. to Entom., 'Zth Ed., p. 458. 



