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An account is given of the karyotypes and male meiosis of the Water Scorpion    Nepa   cinerea    Linnaeus, 1758 and the Water Stick Insect    Ranatra   linearis    (Linnaeus, 1758) (  Heteroptera  ,   Nepomorpha  ,   Nepidae  ). A number of different approaches and techniques were tried: the employment of both male and female gonads and mid-guts as the sources of chromosomes, squash and air-drying methods for chromosome preparations, C-banding and fluorescence  in situ  hybridization (FISH) for chromosome study. We found that    N.   cinerea    had a karyotype comprising 14 pairs of autosomes and a multiple sex chromosome system, which is X 1 X 2 X 3 X 4 Y (♂) / X 1 X 1 X 2 X 2 X 3 X 3 X 4 X 4  (♀), whereas    R.   linearis    had a karyotype comprising 19 pairs of autosomes and a multiple sex chromosome system X 1 X 2 X 3 X 4 Y (♂) / X 1 X 1 X 2 X 2 X 3 X 3 X 4 X 4  (♀). In both    N.   cinerea    and    R.   linearis   , the autosomes formed chiasmate bivalents in spermatogenesis, and the sex chromosome univalents divided during the first meiotic division and segregated during the second one suggesting thus a post-reductional type of behaviour. These results confirm and amplify those of  Steopoe (1925 ,  1927 ,  1931 ,  1932 ) but are inconsistent with those of other researchers. C-banding appeared helpful in pairing up the autosomes for karyotype assembly; however in    R.   linearis    the chromosomes were much more uniform in size and general appearance than in    N.   cinerea   . FISH for 18S ribosomal DNA (major rDNA) revealed hybridization signals on two of the five sex chromosomes in    N.   cinerea   . In    R.   linearis   , rDNA location was less obvious than in    N.   cinerea   ; however it is suggested to be similar. We have detected the presence of the canonical “insect” (TTAGG)  n   telomeric repeat in chromosomes of these species. This is the first application of C-banding and FISH in the family   Nepidae  .

A chromosomal analysis of Nepa cinerea Linnaeus, 1758 and Ranatra linearis (Linnaeus, 1758) ( Heteroptera , Nepidae )