Melasma Overview. Patches of melasma are darker than other areas of skin because they have more pigment. The cells that produce pigment in the skin are called melanocytes. Ultraviolet radiation, or UV rays, from the sun stimulate melanocytes to produce pigment.
The human testicle .The two muscles that regulate the temperature of the testes are the dartos andcremaster muscles:â¢ Dartos Muscle The dartos muscle is a layer of smooth muscle fibers in the subcutaneous tissue of thescrotum (surrounding the scrotum).
Testicles might be outside the body because temperature influences the sex of human children. A temperature-sensitive gender switch that makes hot sperm male could be a relic from our evolutionary past, argue John McLachlan and Helen Storey, citing evidence that more males are born in hot climates.Temperature determines sex in many reptiles.For example, alligators that develop at or below 30 ÂºC turn out to be female, whereas hotter eggs yield males. Such a system wouldn't work in mammals: they maintain a constant body temperature and carry their young within.or example, it might be just as easy to move the temperature switch to a hotter point as to avoid it by moving testicles outside the body. But the idea that the sex switch is still there is testable, argues McLachlan.