168 EVENINGS AT THE MICEOSCOPE. 



Horse-flies or Whame-flies {Tahanus), whicli are so 

 numerous in the latter part of summer flying around 

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

 They are continually alighting on the objects of their 

 attentions, and though driven away, returning 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 eflective, that Heaumur 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, brilliantly clear and translucent. The 

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

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

 dibles are narrow lancets ; of which one edge near the 

 tip is beset with reverted saw-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 

 mMxillcB, which are the principal cuttiug 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 



