Epididymis. Transmission electron micrograph (TEM) of the ultrastructure of epididymal epithelium showing the tips of tall columnar cells extending towards the lumen of the epididymal tubule. This type of epithelium is classified as pseudostratified columnar epithelium. Many stereocilia project into the lumen. The epididymis is a 7-metre-long coiled tube that lies behind each testis, receiving sperm from them. The sperm mature as they pass slowly through this tube. Magnification: x4000 when printed at 10cm.