174 BUKEAU OF ANIMAL INDUSTRY. 



In some cases Avhat appears as a tumor is an impiisoned and undevel- 

 oped ovum, which has grafted itself on the fetus. These are usually 

 sacculated and may contain skin, hair, muscle, bone, and other natural 

 tissues. The only course to be pursued in such cases is to excise the 

 tumor, or, if this is not feasible, to perform embryotomy. 



MONSTKOSITIES. 



Monstrosity in the foal is an occasional cause of difficult parturition, 

 especially such monsters as show excesshe development of some part 

 of the bod}', a displacement or distortion of 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 abnormal!}- small — dwarfed head, liml>, 

 trunk, etc. 



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

 limbs, etc. 



{■i) 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. 



(G) 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. 



(S) Monsters through imperfect differentiation of sexual organs — 

 hermaphrodites. 



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

 etc. 



Causes. — The causes of monstrosities appear to bo 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 arc associated with too close breeding, the powers of sj'mmet- 

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

 incompatibility is developed, near relatives failing to breed with each 

 other. Mere arrest of development of a part ma}^ arise from acci- 

 dental disease of the embryo; hence vital organs are left out, or por- 

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

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

 ing started independently from a separate ovum, but the one having 

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

 oped 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 



