Which structure is involved in the production of sperm cells in males?

The testicle, or testis, is the primary structure responsible for the production of sperm cells in males. Each testicle contains seminiferous tubules where spermatogenesis occurs, the process by which sperm cells are produced from germ cells. Hormones such as testosterone also play a crucial role in this process, and the testicles are also responsible for producing this hormone.

The vas deferens, prostate gland, and ejaculatory duct are all important components of the male reproductive system, but their roles differ significantly from that of the testicle. The vas deferens transports sperm from the epididymis to the urethra during ejaculation. The prostate gland contributes fluid to the semen, which nourishes and protects sperm. The ejaculatory duct serves as a passageway for sperm to enter the urethra and mix with seminal fluid, but does not participate in the actual production of sperm. Thus, the testicle is the correct answer, as it is where sperm are produced.