HOLLAND: SIPHONAPTERA 585 



publications by the microfilm process, thus enabling students to work while far 

 removed from major libraries. 



As the species of any given region become better known, more attention will 

 be devoted to the study of their biology and ecology. Compared to the number 

 of described adults, only a small percentage of flies are known in their early 

 stages and most of these are in groups of medical or economic importance. Simi- 

 larly, under the impact of the so-called "New Systematics," increased attention 

 will be devoted to a critical analysis of supposedly valid species in relation to 

 clines and infraspecific categories. This analysis will result in a reduction in 

 the number of supposed species but should be compensated for by the discovery 

 of still unknown valid species. 



These are merely indications of some of the problems that must be consid- 

 ered in the future. A fascinating field awaits the young entomologist who de- 

 cides to devote his life and energies to a study of the Diptera. 



SIPHONAPTERA! 



George P. Holland^ 

 Sustematic Entomology Unit, Division of Entomology, Ottawa, Canada 



The fleas constitute one of the smaller orders of holometabolous insects. 

 About 1,350 species and subspecies, belonging to approximately 200 genera, are 

 recognized at this time. 



In the adult stage, fleas are ectoparasites of mammals or birds. Their small 

 size, the difficulty of collecting them (except for a few species!), and the lack 

 of suitable techniques and equipment for preparing and examining specimens 

 made them unattractive subjects for study a century or more ago. It is possible, 

 too, that in those early times the sordid circumstances generally associated with 

 fleas discouraged attention from potential students, who turned their talents 

 to problems involving more aesthetic creatures. Ferris (1951) quotes Denny 

 (1842) concerning lice, which were similarly regarded: "... the author has 

 had to contend with repeated rebukes from his friends for entering upon the il- 

 lustration of a tribe of insects whose very name was sufficient to create feelings 

 of disgust." Certainly, by 1853, fewer than 30 specific names for fleas had been 

 proposed, and of these only about 17 are now considered valid. 



Linnaeus recognized only two species of fleas, the so-called human flea, Pulex 

 irritans, and the chigoe, P. (now Tiinga) penetrans. In the early nineteenth 

 century, the familiar "domestic" species from European dogs, cats, rats, house 

 mice, and chickens were described by Curtis, Bouche, Bosc d'Antie, Schonherr, 

 and Schrank. A few species from endemic European moles, hedgehogs, bats, 

 badgers, squirrels, and birds were named during this period also, as well as an 



1. Contribution No. 3054, Division of Entomology, Science Service, Department of 

 Agriculture, Ottawa, Canada. 



2. Head, Systematic Entomology. 



