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Recently, changes in cohesion of epididymal spermatozoa were reported in the flying squirrel (Martan & Hruban, 1970), grey and fox squirrels (Martan, Adams & Perkins, 1970), chinchilla (Martan, 1970a) and several other mammals, including primates (Martan, 1970b). Formations in which spermatozoa adhered tightly together by their tails or tails and heads were called cylindrical bodies. This article presents some additional observations and speculations on the formation and development of cylindrical bodies. The materials and methods involved have already been described in the above mentioned articles. Stereocilia of principal cells protruding into the epididymal duct substantially reduce the size of the lumen. The proximal portion of the ductus epididymidis may therefore be regarded as having two lumina which differ considerably in diameter; a lumen limited by the apical parts of the epithelial cells and a reduced lumen (Reid & Cleland, 1957) bordered by the tips of the stereocilia (Pl. 1, Figs. 1 to 4). Risley (1963) states that spermatozoa are propelled along the epididymal canal by smooth muscle contractions which cause movement of the fluid inside the lumen towards the distal portion of the duct. While the fluid can flow through the lumen proper, movement of the spermatozoa is restricted by the stereocilia to the reduced lumen (Pl. 1, Figs. 1 to 4). The flow of spermatozoa through the reduced lumen may help to orientate them along their long axis and concentrate them into closer promixity so that, through cohesion of their tails, the formation of cylindrical bodies begins (Pl. 1, Fig. 2). The length of the ductus epididymidis travelled by spermatozoa in these closely formed cylindrical bodies and the epididymal segment in which cylindrical formations first appear differ according to species (Martan, 1970b). However, all cylindrical bodies once formed seem to grow in diameter (PI. 1, Figs. 2 to 4) and in length (PI. 1, Figs. 5 and 6) before they break up. We propose that, in order to grow in both directions, additional spermatozoa must adhere to the already formed cylindrical body. These spermatozoa, which are released later from the testis than those already in the epididymidis, catch up with the freshly built cylindrical body somewhere in the proximal part of the duct. As the cylindrical formation is propelled by smooth muscle contractions along the reduced lumen of the epididymal duct, the stereocilia could exert a dragging

THE FORMATION AND DEVELOPMENT OF THE CYLINDRICAL BODIES IN THE MAMMALIAN EPIDIDYMIS