168 EVENINGS AT THE MICROSCOPE. 



Horse-flies or Wliam-e-flies {Tdbanus), M'liicli are so 

 numerous in tlie latter part of summer flying around 

 horses, and men too, if we intrude upon their domains. 

 They are continually alighting on the ohjects of their 

 attentions, and thoui^h driven awav, retuniins: with 

 annoying pertinacity to the attack. You may always 

 recognise them by the brilliant metallic hues — reds, yel- 

 lows, and greens, — with which their large eyes are 

 painted, often in stripes or bands. These are voracious 

 blood-suckers ; and, as might be supposed from their 

 propensities, they are well furnished with lancets for 

 their surgery. Here you may see their case of instru- 

 ments, which are so effective, that Keaumur tells us, 

 that having compelled one to disgorge the blood it had 

 swallowed, the quantity appeared to him greater than 

 the whole body of the insect could have been supposed 

 capable of containing. 



All the parts here are formed of the common amber- 

 coloured chitine, brilliant! v clear and translucent. Tlie 

 upper lip forms a sort of straight sheath, in which all 

 the other parts are lodged when not in use. The man- 

 dihles are narrow lancets ; of which one edge near the 

 tip is beset with reverted saM'-teeth, and the opposite 

 edge with excessively sharp points standing out at right 

 angles, while the surface is roughened with lozenge- 

 shaped knobs set in regular rows. Below these are the 

 m^axillcB, which are the principal cutting instruments ; 

 these are shaped like a carving-'knife with a broad 

 blade, strengthened at the basal part of the back by a 

 thick ridge, but brought to a double edge near the tip. 

 The back-edge is perfectly fine and smooth, so that the 

 highest powers of the microscope can only just define 

 its outline ; while the other edge is notched into teeth 



