Light micrograph of a normal human testis, showing a cross section through the coiled system of seminiferous tubules. Each tubule, outlined by a continuous brown line, the basement membrane, holds a population of spermatogenic cells of differing maturity. Next to the membrane are the least mature spermatogonia, seen as black dots. They give rise to spermatocytes (brown dots), then spermatids, & finally spermatozoa (brown layer at tubule centre). Around the tubules lies the areolar tissue, source of testosterone (hormone). Black fibrous lines within this are blood vessel walls. Magnification: x25 at 35mm size.