MICROSCOPIC OBJECTS. 87 



Fig. 173. Skin-Parasite from Human nose (Demodex 

 folliculorum), x 200. 



The exact position, as regards the classification of this 

 parasite, is rather doubtful ; at present it is classed under the 

 family Acarea. On the nose and the parts adjacent, it is 

 generally to be seen in large numbers ; its presence is always 

 denoted by a minute black spot. The characters of the genus 

 are : Legs terminated by four or five claws ; no acetabula ; 

 abdomen annulose. 



On the skin that contains these parasites being pressed, 

 from each black spot proceeds a small quantity of mattery 

 substance ; this contains the parasite, and also often a number 

 of ova. The mass may be placed at once in the carmine-dye, 

 and then transferred to a drop of glycerine ; next place it on 

 a glass slide, cover with thin glass, and then gently press the 

 dyed matter, after which, if a |-inch power is used, the para- 

 site will be distinguished from the surrounding mass. 



Fig. 174. Eggs of Earth-mite (Tetranychus lapidum), x40. 



The beautiful eggs of this mite may often be found on the 

 inside of the rough pieces of bark that are commonly seen 

 on old Elder trees &c ; they are also found on stones. The 

 description of the species is : Legs slender, anterior very 

 long ; eyes three on each side ; several rows of white spots 

 upon the back and margins of the body. 



The eggs show best when mounted in a dry opaque cell. 



