Spermatozoa formed in the testis enter the caput epididymis, progress to the corpus, and finally reach the cauda region, where they are stored. Sperm entering the caput epididymis are incomplete—they lack the ability to swim forward (motility) and to fertilize an egg. Epididymal transit takes 2 to 6 days in humans and 10-13 in rodents. During their transit in the epididymis, sperm undergo maturation processes necessary for them to acquire motility and fertility. Final maturation ("capacitation") is completed in the female reproductive tract.