New life could not be created without the process that happens inside these colorfully labeled structures. The small round shapes in this image of mouse tissue are formed by Leydig cells, which produce male steroid hormones within the testes. These are contained by the seminiferous tubules, seen here in cross-section, within which the process of spermatogenesis, the production of individual sperm cells, occurs. Understanding of healthy and disordered fertility is aided by anatomical studies that rely on images like this one.