The spermatogenesis of Dictyocaulus filaria (Nematoda, Trichostrongyloidea).

A cytological study was carried out, using male Dictyocaulus filaria, that revealed the diploid number of chromosomes was 2n = 11 and the sex determining mechanism was XO. The behaviour of the chromosomes in the different stages of meiosis was also investigated. Cross, open ring and rod bivalents were observed in diakinesis. The chromosomes appeared to be acrocentric since they acquired a radial disposition in Metaphase-II. The chiasma frequency was 1 and the nucleolus-organizing region was located at the ends of the chromosomes.