The epididymis of Anser melanotus consists of three components, the rete testis, vasa efferentia, and epididymal tubules. The histological structure and the relationships between the three components of avian epididymis are similar to those existing in the mammalian epididymis. The epididymis shows periodic changes in its histological structure, which are parallel to the changes in the testis.

The rete testis consists of wide, anastomosing, cavernous channels, the rete tubules, lines with a simple non-secretory epithelium of cuboidal and columnar non-ciliated cells. During the breeding season the diameter of the rete tubules undergoes an appreciable increase. The internal epithelium becomes squamous through considerable distension.

The efferent ducts are lined by groups of columnar ciliated cells alternating with non-ciliated cubical cells, both the types showing secretory activity in the progressive and reproductive phases of the testicular cycle. The internal epithelium of the efferent ducts is thrown into longitudinal folds, leading to the formation of crests and crypts, which give a festooned appearance to the lumen.

The epididymal tubules are lined with columnar ciliated cells. During the onset of reproductive period, the epithelial cells of the epididymal tubules hypertrophy and become secretory. The secreted droplets are discharged into the tubule lumina. During the breeding season the epididymal tubules are filled with sperms. In the refractory phase of the testis cycle the epididymal tubules present an embryonic appearance and have no limiting membrane. Groups of cells similar to those which constitute the lining of the tubules can be seen. These cords of cells become bigger by the division of the pre-existing cells and lumina then appear in the centre, leading to the formation of new tubules.

The epididymal secretion gives a stimulus to the spermatozoa different from that given by the testis; it brings about the ripening changes in the spermatozoa.

There is no influence in the epididymis which can indefinitely preserve the vitality of sperms. The unejaculated spermatozoa left over in the epididymis after the breeding season is finished, either undergo dissolution in the lumina of the tubules or penetrate into the epithelial lining of the efferent ducts and epididymal tubules or even into the surrounding connective tissue, to undergo degeneration there.

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