[Peculiarities of thoracic and abdominal combs of fleas (Siphonaptera)]

The structure of pseudosetae, spinelets, and spines of combs (ctenidia) was studied by means of light and SE microscopy in 80% of genera and subgenera of the World fauna. It is found out that peculiarities of ctenidiae in the prothorax and in tergites of the abdomen are characteristics of families and infraorders of fleas. Some characters of ctenidiae found in certain flea genera are reductions and apparently caused by habitation in some extremal conditions. An absence of ctenidiae in the unfraorder Pulicomorpha is compensated by more developed posterior margin of prothorax and general abbreviation of all thoracal segments. Reasons of ctenidiae absence, which is observed in certain genera of the infraorders Ceratophyllomorpha, Pygiopsyllomorpha and Hystricopsillomorpha associated with the same hosts, is not clear. It is confirmed, that distance between ctenidiae in different flea species associated with the same species host species, however it is recovered, that this distance correlates with the diameter of most thin hair of host. In some flea species the distance between ctenidia spices in females is larger, than in males. It is found, that sexual dimorphism by this character may not be expressed in certain species of closely related species group of fleas. It is suggested that ctenidiae were present even in the common ancestor of fleas. The hypothesis on origin of spines and pseudosetae from setae of the posterior walls of toracal and abdominal segments in the common ancestor of fleas is proposed.