171 



development being interfered with, just as in other cases a sexnal 

 incompatibility is developed, near relatives failing to T)i'eed with each 

 other. Mere arrest of development of a part may arise from acci- 

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

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

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

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

 become embedded in the semi-fluid mass of the other and having 

 developed there simultaneously with it, but not so largely nor x^er- 

 fectly. In many cases of redundance of jparts, the extra i^art or mem- 

 ber has manifestly develojped from the same ovum and nutrient cen- 

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

 nev\' tail will grow out in a newt when the former has been cut off. 

 In the early embryo, v/ith its great powers of develoxjment, this factor 

 can operate to far greater x^urpose than in the adult animal. Its 

 influence is seen in the fact x^ointed out bj' St. Hilaire that such 

 redundant x^arts are nearly always connected vrith the corresx^onding 

 portions in the normal f cetus. Thus sux^erfluous legs or digits are 

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

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

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

 back. All this suggests the develox)mont of extra x>arts from the 

 same x^i'imary layer of the impregnated and develox^ing ovum. The 

 effect of disturbing conditions in giving such wrong directions to the 

 develoxomental forces is v/ell shown in the experiments of St. Hilaire 

 and Valentine in varnishing, shaking, and otherwise breaking up the 

 natural connections in eggs, and thereb}" determining the formation 

 of monstrosities at will. So, in the mammal, blows and other inju- 

 ries that -detach the foetal membranes from the walls of the womb or 

 that modify their circulation Iw inducing inflammation are at times 

 followed by the develox)ment of a monster. The excitement, mental 

 and x>hysical, attendant on fright occasion all}' acts in a similar way, 

 acting x^robably through the same channels. 



The monstrous forms likely to interfere with x^ai'turition are such 

 as from contracted or twisted limbs or sx)ine, must be presented 

 double; where supernumerary limbs, head, or body must apx:)roach 

 the x^assages v\'ith tlie iiatural ones; where a head or other member 

 lias attained to an unnatural size ; Avhere the body of one foetus has 

 become inclosed in or attached to another, etc. 



Extraction is sometimes possible by straightening the members and 

 securing such a x^resentation as will reduce the xJi'esenting mass to its 

 smallest and most wedge-like dimensions. To effect this it may be 

 needful to cut the flexor tendons of bent limbs or the muscles on the 

 side of a twisted neck or body; and one or more of the manipulations 

 necessary to secure and bring u]) a missing member may be requii-ed. 

 In most cases of monstrosity by excess, however, it is needful to 



