245 



Modifications of the Legs in some Dipterous Flies. 

 By W. Wesche, F.E.M.S. 



{Read January 17th, 1902.) 



Plates 13 and 14. 



This may perhaps be thought a subject more fitted for a society 

 •devoted to Entomology than to Microscopy, but as the structures 

 I am about to bring under notice are all microscopic, I plead 

 their small size as justification for submitting them to the 

 Quekett Club. 



To compensate for the absence of nerves in the chitinous 

 covering of insects, many hairs and bristles are present, which 

 are placed in sockets, and no doubt convey some kind of 

 sensation when touched or excited, as they have a connection 

 with the nervous system. Their number, size, and arrangement 

 vary in an infinite degree in the different families and species. 



When on the legs, delicate hairs are used for three purposes : 

 (1) As brushes to keep the antennae, and the hairs on the body, 

 head, and eyes, clean and sensitive. Such an arrangement is 

 found on the fore tarsi of the larger house-fly, Musca doniestica ; * 

 {2) As pads, as in PlcUichi7'us, which I shall refer to later on ; 

 (3) As floats, as in Dolichopics, where the tomentum, or down, 

 on the tarsi is so fine, that it holds the air and enables the insect 

 to glide on the surface-film of water. 



In other cases the hair is stronger, and is modified into bristles, 



* A similar brush is found on the fore tarsi of the hive bee (Aj)is 

 mellifica), and of most of the Hymenoptera. So important to these 

 insects is the care of the antennae, that, in addition to this brush, special 

 cavities have been hollowed out of the first fore tarsi, which are fitted 

 with an arrangement of stiff hairs in the shape of semicircular combs, 

 through which the antennae are drawn. (See Cheshire on the Hive Bee.) 



