Results of an investigation of the pupal development and adult anatomy of the male genitalia of Xenopsylla cheopis (Rothschild, 1903) are presented as well as descriptions and comparative analyses of the male genitalia in the 24 genera for which males are known. The first cladogram of the pulicoid taxa is presented. The 258 figures are in the form of line drawings as well as light micrographs and both scanning and transmission electron micrographs;The adult anatomy of the genitalia of male X. cheopis is described in detail, and is shown to be identical in basic structure with that reported in other families. Pupal development of the genitalic rudiments is comparable in all essentials to that reported for ceratophyllid fleas and is consistent with the general pattern of development described for the panorpoid complex as a whole;The major results of the comparative study are as follows: The basic division is based on clasper anatomy and is between the Rhipimorpha (fr. Gk.: fan ) and the Thermastromorpha (fr. Gk.: pincer). The Rhipimorpha is predominantly restricted to the New World, the Thermastromorpha to the Old. Neotunga is not closely allied to the tungids. The Tunginae is best understood as the sister group to the Hectopsyllinae. The existing subfamilies are all likely monophyletic with the possible exception of the Archaeopsyllinae which may be paraphyletic with respect to the Xenopsyllinae. Xenopsylla is polyphyletic and should be broken into three separate genera. Moeopsylla exhibits a very aberrant genitalic anatomy, and should be transferred from the Pulicinae, and elevated to the rank of subfamily. The taxon is of uncertain affinities, but is treated here as the sister group of the Archaeopsyllinae + Xenopsyllinae. During the course of this study a new genus was discovered in material from the British Museum, and will be described in a later paper. The taxon is a member of the Xenopsyllinae and is allied with Procaviopsylla and Pariodontis.