Human spermatids. Transmission electron micrograph (TEM) of a section through a human testis (testicle), showing two elongating spermatids. Here, the spermatid germ cells are undergoing spermiogenesis - the final stage of spermatogenesis, which sees the maturation of spermatids into mature, motile spermatozoa (sperm cells). The wedge-shaped nuclei (black) contain the DNA/chromatin condensed and clustered as it is compacted into the emerging shape of the sperm head. Magnification: x42,000, when printed 10 centimetres wide.