Human terata are now commonly classified in four groups: (1) Hemiteratic; (2) Heterotaxic; (3) Hermaphroditic; and (4) Monstrous. Hemiterata are giants, dwarfs, persons showing anomalies in shape, color, closure of embryonal clefts, in absence or excess of digits, or like defects. The Heterotaxic group are persons whose left or right organs are reversed in position. A true Hermaphrodite would have the complete reproductive organs of both sexes, but such an individual has not been observed. There is never any question of double personality in hermaphrodites. Terata more properly so called may be single, double, or triple; and single monsters may be autositic or independent of another fetus, or they may be omphalositic, dependent upon another which is commonly well developed and which supplies blood for both through the umbilical vessels. There are four genera of autositic single monsters, with eight species and thirty-four varieties. Of the _monstra per defectum_ the commonest are caused by a failure of closure in the embryonal medullary canal, which leaves part of the brain and spinal cord or their bony covering lacking. Some terata, as the Acephalia, have no brain or spinal cord, but they die in the fetal stage. The Anencephalia may have a spinal cord, a medulla oblongata, and parts of the basal ganglia, but the cerebral hemispheres are wanting. Such monsters are sometimes born at term and live for several days: they cry, suckle, show some reflexes and a sense of pain, and move the arms and legs.