Sperm maturing in testis, Transmission electron micrograph (TEM) of a section through a seminiferous tubule in a testis. The sectioned tissue shows stages of sperm cell development as the cells move from bottom to top. At bottom, on the basement membrane, are several spermatogonia (immature sperm cells, round). Above these are primary spermatocytes, followed by the spermatids. One of the later stages are the fully elongated spermatids (top, with white areas), near the tubule lumen, with thin fusiform-type nuclei. Magnification: x1000 when printed at 10 centimetres tall.
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