452 MEDICAL ENTOMOLOGY 



Mespsternite with a rod-like incrassation from the insertion of 



the coxa upwards ........ Xenopsylla. 



12. Club of antenna not symmetrical, the proximal segments 

 sloping backwards. Genal process with only one or two 

 bristles Rhopalopsyllus. 



Club of antenna segmented all round, symmetrical. Hind 

 coxa without comb. Antennal groove closed behind. Anti- 

 pygidial bristle absent in both sexes. Claws of tarsi without 

 distinct basal hook. No anal stylet in female . . . Lycopsylla. 



GENUS PULEX, L. 



Pulex irritans, L., the human flea, is the type and perhaps the only 

 species of this genus. It is found practically all over the world, and 

 though man is the favourite host, it is occasionally found on rats, mice, 

 and other mammals, among which may be noted the badger. It is not 

 the only flea which attacks man, for the cat and dog fleas frequently 

 do so. 



A very nearly allied species, which appears to be confined to Mexico, 

 has been described by Baker. Its habit is similar to that of P. irritans, 

 from which it may be distinguished by the fact that whereas in the 

 common human flea the labial palpi are one- half the length of the 

 anterior coxae, in dugesli they are three-fourths the length or more. 



In the early days of the study of fleas a very large number of species 

 were included in the genus Pulex, but with a general increase in our 

 knowledge of the family these have been gradually allocated to other 

 genera created for their reception, until now only the two species given 

 above remain, and of these dugesli may perhaps only be a local race, the 

 characters distinguishing the two being of doubtful specific value. 



Pulex is regarded by Jordan and Rothschild as the most specialized 

 of the Pulicidae, and as approaching nearer to the Sarcopsyllidae 

 than any other. It is undoubtedly an old world form, having spread 

 from its original habitat with civilized man on his travels ; it was probably 

 introduced in this way into the New World, with the fleas of which it 

 is not closely allied. Its introduction into some of the more remote 

 parts appears, however, to be of comparatively recent date. 



Some diagnostic points other than those given in the key may be u'se- 

 ful in distinguishing it in doubtful cases. The mandibles are broad, 

 short, and deeply serrate. The rostrum is shorter than the maxillary 

 palpus, reaching about half-way down the fore coxa. The thoracic 

 tergites are short, each with one row of bristles. The mesosternum 

 (Plate LV, fig. 1) is characteristic, very narrow, its ventral edge strongly 

 oblique, the stigma not covered entirely ; there is no rod-like incrassation 



