INSECTS : THEIR FEET. 115 



appearance of adhering to the glass by a viscid material 

 than by any pressure of the atmosphere, and it is so far in 

 favour of Mr. BlackwalTs hypothesis, on which one might 

 conjecture that from some cause (perhaps of disease) the 

 hairs of the pulvitti had poured out a greater quantity of 

 this viscid material than usual, and more than the muscu- 

 lar strength of the fly was able to cope with." * 



In the foot of the fly tinder 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 

 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 be- 

 neath 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, mem- 

 branous, and transparent, and when a strong light is re- 

 flected through them, we see their structure under this 

 power of 600 diameters very distinctly. 



The inferior surface of the palm, on which we are 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 by 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 the fly is walking, and is there slightly 

 hooked and enlarged into a minute fleshy bulb. Those 

 from the areas near and at the margins of the palms more 

 and more arch outwards, so that the space covered by the 

 bulbs of the filaments is considerably greater than that of 

 the palm itself. 



* " Introd. to Entom.," 7th Ed., 458. 



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