DISEASES OF THE GENERATIVE ORGANS. 195 



parts, or a redundancy of parts, as in double monsters. Monsters 

 may be divided into — 



(1) Monsters with absence of parts — absence of head, limb, or 

 other organ. 



(2) Monsters with some part abnormally small — dwarfed head, 

 limb, trunk, etc. 



(3) Monsters through unnatural division of parts — cleft head, 

 trunk, limbs, etc. 



(4) Monsters through absence of natural divisions — absence of 

 mouth, nose, eyes, anus, confluent digits, etc. 



(5) Monsters through fusion of parts — one central eye, one nasal 

 opening, etc. 



(6) Monsters through abnormal position or form of parts— curved 

 spine, face, limb, etc. 



(7) Monsters through excess of formation — enormous head, super- 

 numerary digits, etc. 



(8) Monsters through imperfect differentiation of sexual organs — '■ 

 hermaphrodites. 



(9) Double monsters — double-headed, double-bodied, extra limbs, 

 etc. 



Causes. — The causes of monstrosities appear to be very varied. 

 Some monstrosities, like extra digits, absence of horns or tail, etc., 

 run in families and are produced almost as certainly as color or form. 

 Others are associated with too close breeding, the powers of symmet- 

 rical development being interfered with, just as in other cases a sex- 

 ual incompatibility is developed, near relatives failing to breed with 

 each other. Mere arrest of development of a part may arise from 

 accidental disease of the embryo ; hence vital organs are left out, or 

 portions of organs, like the dividing walls of the heart, are omitted. 

 Sometimes an older fetus is inclosed in the body of another, each 

 having started independently from a separate ovum, but the one 

 having become embedded in the semifluid mass of the other and hav- 

 ing developed there simultaneously with it, but not so largely nor 

 perfectly. In many cases of redundance of parts the extra part or 

 member has manifestly developed from the same ovum and nutrient 

 center with the normal member to which it remains adherent, just as 

 a new tail will grow out in a newt when the former has been cut off. 

 In the early embryo, with its great powers of development, this fac- 

 tor can operate to far greater purpose than in the adult animal. Its 

 influence is seen in the fact pointed out by St. Hilaire that such 

 redundant parts are nearly always connected with the corresponding 

 portions in the normal fetus. Thus superfluous legs or digits are 

 attached to the normal ones, double heads or tails are connected to a 

 common neck or rump, and double bodies are attached to each other 

 by corresponding points, navel to navel, breast to breast, back to 



