"The male fox's scrotum is held up close to the body with the testes inside even after they descend. Like other canines, the male fox has a baculum or penile bone. The testes of red foxes are smaller than those of Arctic foxes. Sperm formation in red foxes begins in August–September, with the testicles attaining their greatest weight in December–February.

Vixens are in heat for one to six days, making their reproductive cycle twelve months long. As with other canines, the ova is shed during estrus without the need for the stimulation of copulating. Once the egg is fertilized, the vixen enters a period of gestation that can last from 52 to 53 days. Foxes tend to have an average litter size of four to five with an 80 percent success rate in becoming pregnant. Litter sizes can vary greatly according to species and environment – the Arctic fox, for example, can have up to eleven kits.

The vixen usually has six or eight mammae. Each teat has 8 to 20 lactiferous ducts, which connect the mammary gland to the nipple, allowing for milk to be carried to the nipple." (WIKIPEDIA)