SPERMATOGENESIS IN A TRICHUROID NEMATODE,TRICHURIS MURIS.II. FINE STRUCTURE OF PRIMARY SPERMATOCYTE AND FIRST MEIOTIC DIVISION

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Abstract
Ultrastructural observations indicate that the primary spermatocyte of Trichuris muris is larger than the spermatogonial stage with an increased cytoplasm to nucleus ratio. The cytoplasm contains an extensive reticular system, mitochondria, numerous free ribosomes and prominent Golgi complexes which may contribute to the formation of a sub-surface, vesicular complex. Although only two spermatocytes were seen to be linked by a cytoplasmic bridge it is suggested that the number of conjoined cells is probably greater. The rearrangement of mitochondria in a ring around the nucleus and the indentation and vesiculation of the nuclear envelope preceeded its disappearance and indicated the onset of meiosis. Centrioles were frequently resolved at this stage. They were composed of nine peripheral doublets surrounded by a dense pericentriolar sheath. Three dense chromatin areas indicative of haploid chromosomes were present in later meiotic stages. Each chromosome was surrounded by a number of mitochondria and there was a clear separation of the chromosome-mitochondrial clusters from the remainder of the cytoplasm. This was particularly evident at telophase when two daughter cells were partially separated by membrane infoldings. This reflects incomplete cytokinesis in the dividing spermatocyte of T. muris and is similar to that described in other trichuroid species. A close association with processes of the non-germinal, sustentacular cells was noted throughout the spermatocyte stage.