MICROSCOPIC OBJECTS. 81 



Fig. 161. A Human Flea, female (Pulex irritans), x 15. 



The human Flea has been drawn chiefly to show its simi- 

 larity to the other species of Flea ; but upon considering the 

 description of the species, which is as follows, it will be found 

 that the structural characters are slightly different : Pitch- 

 brown ; head shining, smooth, pectinate fringe absent ; legs 

 pale ; femora of the posterior legs with hairs inside ; fifth 

 joints of the tarsi of the anterior pair of legs the largest, and 

 the first joints of the posterior tarsi the longest. The larvae 

 of this and other Fleas form interesting objects. 



This species may be mounted in the same manner as the 

 preceding. 



Fig. 162. Lancets of Human Flea (Pulex irritans), x 100. 



Causing so much irritation, as these fine instruments do, 

 when forced into our skin, we cannot but admire, after a 

 microscopic view of them, their fineness of form and struc- 

 ture. The lancets, or mandibles, are on the right-hand side 

 of the drawing, and may be distinguished by their serrated 

 edges. Between them is the labrum, or the suctorial organ ; 

 the two antennae -like bodies with four joints, at each side of 

 the drawing, are the maxillary palpi ; the shield-like bodies 

 represent the maxillae, and the 4-jointed labial palpi placed 

 between these are the organs in which the lancets are 

 sheathed when at rest. 



The lancets, with the surrounding parts, require very care- 

 ful mounting. The best plan, after they are cut off from the 

 head of the Flea, is to place them in the centre of a glass 

 slide, in a drop of balsam about the size of a pin's head, then 

 with a fine needle to place them in their proper positions, 

 after which, let the drop dry under a glass shade, so as to 

 keep off the dust. When quite dry, place the thin cover on, 

 and let diluted Canada balsam run in by capillary attraction, 

 so as not to disturb the objects; finish as usual. 



M 



