(1) From absence of parts—absence of head, limb, or other organ—arrested development.
(2) From some organ being unnaturally small, as a dwarfed head, limb, trunk, etc.—arrested development.
(3) From unnatural division of parts—cleft lips, palate, head, trunk, limbs, etc.—abnormal growth.
(4) From the absence of natural divisions—absence of mouth, nose, eye, anus; the cloven foot of ox or pig becomes solid, like that of the horse, etc.—confluence of parts which are rightfully separate.
(5) From the fusion of parts—both eyes replaced by central one, both nostrils merged into one central opening, etc.—confluence of parts.
(6) From unnatural position or form of parts—curved nose, neck, back, limbs, etc.—lack of balance in the growth of muscles during development.
(7) From excessive growth of one or more organs—enormous size of head, double penis, superfluous digits, etc.—redundancy of growth at given points.
(8) From imperfect differentiation of the sexual organs—hermaphrodites (organs intermediate between male and female), male organs with certain feminine characters, female organs with certain well-marked male characters.
(9) From the doubling of parts or of the entire body—double monsters, doubled heads, doubled bodies, extra limbs, etc.—redundant development. ([Pl. XIX], figs. 1, 2, 3.)