172 EVENINGS AT THE MICROSCOPE 



per lip forms a sort of straight sheath., in which all the 

 other parts are lodged when not in use. The mandibles 

 are narrow lancets; of which one edge near the tip is beset 

 with reverted saw-teeth, and the opposite edge with exces- 

 sively sharp points standing out at right angles, while the 

 surface is roughened with lozenge -shaped knobs set in 

 regular rows. Below these are the maxillce, 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 micro- 

 scope can only just define its outline ; while the other edge 

 is notched into teeth so delicate that twelve of them are 

 cut in the length of a ten-thousandth part of an inch ; and 

 yet they are quite regular and symmetrical in length, 

 height and form! I know of no structure of the kind 

 which equals this. These teeth are continued throughout 

 the inner edge of the blade from the tip to the base, and 

 are about eight hundred in number; though the length of 

 the entire blade is only such that upward of a hundred 

 and fifty of them, if laid end to end, would not reach to 

 the extent of an inch! 



The office of these wonderful instruments is doubtless 

 to cut and enlarge the wound within, and thus promote 

 the flow of blood. The whole apparatus is plunged into 

 the flesh of the victim horse or man; then the maxillce 

 expand, cutting as they go, and doubtless working to and 

 fro as well as laterally, so as to saw the minuter blood- 

 vessels. At the same time the mandibles, with their saw- 

 teeth on one side, and pricking points on the other, work 

 in like manner, but seem to have a wider range. Finally, 



