PULEX IRRITANS. 89 



1. The common Flea = Pulex irritans sive vulgaris. 



The head of this reddish-brown animal which is so widely 

 diffused over the earth, but unknown in Australia, is short, 

 shield-shaped, formed of one piece, not toothed on the margins; 

 the antennae are short, and concealed in a pit behind the eyes, 

 and therefore often overlooked and mistaken. The oral organs 

 consist of a bristle-like tongue, which is covered by two maxillae 

 of the form of two sword-blades. These maxillae are covered by 

 two very narrow mandibles, which lie together to form a sheath, 

 and are toothed on their convex tipper surface, like files. On the 

 sides of the proboscis, and somewhat covering the base of the four- 

 jointed antenna, are two massive brown scales; these are usually 

 called labial palpi, and probably form a sort of cleft upper lip. The 

 labium covers the proboscis from beneath, and like the upper lip 

 appears to be cleft. It is hollow above, acute and hairy in front. 

 The thorax, which is probably provided with two pairs of stig- 

 mata, consists of three separate segments, each of which, espe- 

 cially the third, bears a pair of long legs, well adapted for leaping. 

 These consist of a strong coxa, with a small trochanter, a strong 

 thigh and tibia, which are all but slightly hairy internally, and of 

 five tarsal joints. The first and longest of these is strongly 

 clothed with hairs internally, without hairs on the outside; the 

 other smaller joints are strongly hairy on both sides, and the last 

 bears two claws. The first pair of feet appears almost to stand 

 on the head. 



The abdomen has ten laterally separated segments, laid over each 

 other like the tiles of a roof, and fringed at the margins. On the 

 penultimate, or ninth segment, called the pygidium, there are 

 spinous hairs inserted in little pits (areolce). Each of these areolse 

 is about 0-012 mill, in breadth, and adorned round the base of the 

 hair with a circle of ten round, bead-like globules. 



Besides its small size, the male is distinguished by the form 

 of the extremity of his abdomen. The upper end of the pygidium, 

 namely, projects as a sharp angle, and the last joint is attached 

 scarcely perceptibly flat to this. By this the end of the abdomen 

 of the male becomes as if cut off" straight and broader. At the 

 same time it appears to me that the pygidium is rather less hairy 

 than in the female, and that the penis is double. At least we 

 always see two brown spiral fibres in the middle of two more 

 membranous, transparent structures, which are swollen up into 



