In the adults of a male adult, testes usually descend into scrotal sacs.The penis is a copulatory organ found in males.Internal fertilization takes place.  Gonoducts head directly to the exterior areas.Mostly viviparous animals are found that give birth directly to the young ones.In the female's uterus development occurs. The embryo has amnion, chorion, and allantois.For the purpose of nourishment, excretion, and respiration, the fetus is fixed by the placenta into the uterine wall.After the birth of young ones, they are nourished with milk for some time.