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The reproductive system ensures the survival of the species. Other systems in the body, such as the endocrine and urinary systems, work continuously to maintain homeostasis for the survival of the individual. An individual may live a long, healthy, and happy life without producing offspring, but if the species is to continue, at least some individuals must produce offspring.
Testes

Transverse section through the seminiferous tubules of the testis.
The spermatogonia, which are the youngest spermatocytes, are closest to the edge of the tubule, and the spermatozoa, or sperm with tails, which are the most mature spermatocytes, are closest to the middle. Spermatogonia are the biggest of the germ cells, and their nuclei are round and made up of small grains.
Seminiferous tubules merge to form rete testis, a network of straight tubules that progress to the epididymis, and then to subsequent ducts, ending with the urethra.