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 maxilla 

 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 which we 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 back- 

 wards. These are the mandibles, and they closely fold 

 together, inclosing another narrower blade, the upper Up, 

 which has its two edges studded with similar points, but 

 in a single row. 



