MICROSCOPIC OBJECTS. 88 



Fig. 175. Itch-insect, female (Sarcoptes scabiei), x 60. 



The Itch-insect belongs to the same family as the Cheese- 

 mite. The parasite is chiefly remarkable for causing the 

 disease called the Itch. The description of the parasite is as 

 follows : Head small,, somewhat narrowed in front ; mandi- 

 bles toothed; anterior two pairs of legs separated from the 

 posterior by a considerable interval : legs short, the anterior 

 two pairs with acetabula or adhesion-disks, 5 -jointed; the 

 posterior 3-jointed, the last joint terminated by a long seta 

 and without acetabula. Male insect about half the size of 

 the female, and with acetabula to the hindermost pair of legs. 



The parasite shows best when mounted in a cell with chlo- 

 ride of calcium or glycerine. 



Fig. 176. Parasite of Watchman-Beetle (Gamasus coleo- 

 ptratorum) , x 20. 



Another parasite of the order Acarina is commonly found 

 on the Dung- or Watchman-Beetle (Geotrupes stercorarius] 

 as it is popularly called. The description of the species is as 

 follows : Anterior coxse attached at a little distance from 

 those of the second pair ; tarsi with two claws and an elegant 

 caruncle ; palpi free, filiform ; mandibles chelate ; ocelli none 

 or indistinct. 



The parasite may be cleaned, dried under pressure, and 

 mounted in balsam as usual ; or it may be mounted in a cell 

 with chloride of calcium, acetic acid, or glycerine. 



