For the first time, the karyotype is described in a representative of the order Zoraptera. Zorotypus hubbardi Caudell (Zorotypidae) have holokinetic chromosomes and male karotype of 2n = 38 (36 + neo-XY). Males possess two follicles in each testis and females have six panoistic ovarioles in each ovary. Oogenesis and, more closely, spermato genesis, including meiosis and sperm formation, have been studied. Based on the presence of panoistic ovaries and holokinetic chromosomes, Crampton's hypothesis that Zoraptera represent a group of Polyneoptera nearest to the origin of Paraneoptera is considered the most plausible.

Males of Hysteropterum albaceticum Dlabola, 1983 and Agalmatium bilobum (Fieber, 1877) display a chromosomal complement of 2n = 26 + X, which is a basic one of the tribe Issini (Issidae). In the present study, silver staining, C-banding and a base specific CMA3 -and DAPI-banding were used with the aim of identifying possible cytogenetic markers and distinguishing between karyotypes with the same chromosome number and no detectable inter-species differences in karyotype structure. We characterized the species studied in terms of the distribution and molecular structure of C-heterochromatin regions and the location of nucleolus organizing regions (NORs). The species are shown to differ considerably in the amount of heterochromatin, its distribution pattern along the karyotypes and its stain ability with DAPI and CMA3.