221 



large hairs. Close to the origin of each claw there is a thin 

 brown plate of similar material to it, which carries a large 

 rounded boss of considerable size. Figs. 21 and 22. This 

 boss or flap forms the segment of a small circle, the convexity 

 being downwards and forwards. Its dorsal surface is smooth, 

 but the convexity is covered with an immense number of 

 long hairs which impart to it the appearance of a brush when 

 seen in profile. Each of these hairs terminates by forming a 

 right angle with itself; thus exposing as large a surface as 

 possible to any plane body. In many cases they have an ad- 

 ditional terminal enlargement. 



These hairs are evidently covered with a viscid secretion, and 

 are usually coated with adherent particles of dust and dirt. 

 In plain words they are sticky. 



The feet have therefore to be cleaned before we can see 

 these hairs to perfection. 



As we shall have to refer to this viscidity hereafter, I will 

 merely stop here to explain the cause of a phenomenon of 

 which the commonest observer is cognizant. 



These little creatures — the house flies — may be frequently 

 seen rubbing their fore legs together as we would wring our 

 hands, their middle pair is as frequently rubbed against the 

 wings or the hinder pair, and the hinder pair are rubbed 

 against the back or each other. At first sight this might be 

 taken for a cleansing of the limbs alone ; an appeal however to 

 facts shows us that it is intended to remove from the bosses all 

 adherent particles of dust, which, by choking them up, pre- 

 vents them from using their feet to perfection. 



A portion of the viscid secretion may be found on the 

 surface of polished glass immediately after a fly has walked 

 over it, provided the foot is clean, or in case the foot is much 

 clogged with dirt it may be traced by the particles left behind. 



In addition to the particular secretion of these hairs, they 

 possess, in common with many other minute linear structures, 

 the power of attracting air very strongly. Whenever then the 



