146 EVENINGS AT THE MICROSCOPE. 



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 

 upwards 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, there is an exceedingly delicate piece beneath 

 all, which seems to represent the labium or under lip. 



In the active and cunning little Flea, that makes his 

 attacks upon us beneath the shelter of the blankets and 

 under cover of night, the piercing and cutting blades are 

 very minute, and have a peculiar armature. They remind 

 me (only in miniature of course) of those formidable flat 

 weapons w r hich w^e often see in museums, the rostrums of 

 the huge Saw-fishes (Pristis) ; a great plate of bone 

 covered with grey skin, and set along each side with a 

 row of serried teeth. Here the blades are similar in form, 

 being long, straight, narrow plates of transparent chitine, 

 set, along each edge, with a double row of glassy points, 

 which project from the surface, and are then hooked 

 backwards. These are the mandibles, and they closely 

 fold together, inclosing another narrower blade, the 

 upper lip, which has its two edges studded with similar 

 points, but in a single row. 



