Abstract
A study of male meiosis has been carried out on air-dried testicular preparations from three insectivore species: Crocidura russula, Neomys anomalus and Talpa occidentalis. Two particularities in relation to the meiotic process were found. The sex-chromosomes show a special allocycly. In the zygotene and pachytene stages, only some cells (a maximum of 50% in some individuals) present a typical sex-vesicle. In the majority of cells in these stages, the X-chromosome appears unfolded, isopycnotic or negatively heteropycnotic, with the ends of the arms together. The Y-chromosome is more condensed and it is associated with the ends of the X-chromosome. At diakinesis and metaphase I the sex chromosomes show end-to-end pairing. A second interesting feature in these species is the existence of spontaneous polymeiosis in a relative high frequency. The origin of this phenomenon, and the influence of these two particularities on fertility and the relation with the phylogeny of these species are discussed.
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