| The present study was carried out by use of anatomical and histological methods toinvestigate the morphological characteristics of testis in yak. A preliminary work onspermatogenesis was also performed by use of histological methods. The followingresults were obtained.(1) The anatomical characteristic of yak testis was generally similar to that of othercattle, excerpt for the weight and size which were significant lower/less than those ofHolstan and yellow cattle. Otherwise, there was only one efferent duct collected to thehead of epididymis.(2) Spermatogenesis of yak was also similar to that of other cattle. The seminiferousepithelium cycle could be divided into eight stages according to the morphological anddistributional characteristics of spermatogenic cell, spermatid and spermatozoon indifferent developing periods.(3) An extremely difference existed about the parameters of quantitative histologybetween the parameter which were obtained from the present study during thetransitional period (November and December) from reproductive season tonon-reproductive season and those from the originally reported reproductive period,including diameter of contorted seminiferous tubules, total number density of germocyte,numerical density of spermatogonia, numerical density of spermatocyte and numericaldensity of spermatids.(4) Degeneration and loss of different types of spermatogenic cells occurred insome extend during the process of spermatogenesis, which could not be identified in thetestis section, but could in epididymis section by light microscopy.(5) The observation on paraffin section of the yak testis in the present studyrevealed that cell assemblage might appear in a undulate sequence duringspermatogenesis, but the undulate sequence were not executed strictly in some district.Some of the spermatogenic cells were displaying a state of delaying or degeneratingcompared with other spermatogenic cells of the same kind in their vicinity.
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