During the mating season, the secretions of the musk glands serve as sex pheromones. They not only attract individuals of the opposite sex, but also stimulate and drive them to mate. There is considerable evidence that the musk glands are closely related to the gonads. First: their activity is cyclical, peaking during the mating season. At this time, they are large and filled with abundant secretion, which is why the animals have the strongest odor during this period. Second: castration suppresses the activity of the musk glands. Castrated animals have a weaker odor and do not attract the opposite sex. However, if sex hormones are administered, the function of the musk glands is restored and the animals once again become attractive to the opposite sex.