MICROSCOPIC OBJECTS. 82 



Fig. 163. A Human Louse (Pediculus vestimenti) . 

 Order Anoplura, x 16. 



The description of this repulsive insect, which has been 

 taken as a type of the order and genus, is as follows: 

 Colour dirty white ; elongate- ovate ; thorax large, not con- 

 stricted from the abdomen ; head much produced ; antennae 

 5 -jointed; mouth with a fleshy rostrum concealed beneath 

 the head, consisting of a soft tubular sheath dilated at the 

 end, where it is furnished with a double row of hooks, and 

 containing a horny tube formed of four setse; abdomen with 

 seven segments indistinctly indicated ; legs all scansorial or 

 prehensile ; length about ^ inch. 



The insect may be mounted in balsam as usual. 



Fig. 164. Parasite of Horse (Trichodectes equi), x 20. 



Other insects of the same order as the preceding are para- 

 sitic upon some quadrupeds, viz. the Horse, Sheep, Ox, Dog, 

 &c., in all about ten species. The characteristics of the 

 genus are : Head subquadrate, with two black spots in 

 front, and a black band on each side ; antennae filiform, 

 3-jointed ; maxillary palpi none, or inconspicuous ; mandibles 

 2-toothed; tarsi 2-jointed, with one claw; abdomen oval. 



The insect usually only requires to be dried between writing 

 or glazed paper, under moderate pressure, soaked in turpen- 

 tine until transparent, and then mounted in balsam. 



