MONS THOSITIES. 1 1 :j 



condition, and partial excess of an organ or region is not infrequent; while 

 excess of parts is far from rare, and may be noted in the vasculai' 

 system, in internal organs, and externally ; more particularly is it 

 remarked in the extremities, when we iiave in some species "polydactyl- 

 ism," and in others " hyperdactylism." It is often observed that an 

 excess in development in one part coincides with defective development 

 in another, as if the balance in formative organization must be main- 

 tained throughout the body. 



With regard to double monstrosities — the result of two fcetuses bein^ 

 accidentally joined together, and fused, as it were, into each other — G. 

 Saint- Ililaire proposed a special law which he designated the laio of 

 similar union or of mutual affinitij. The result of this law is the pro- 

 duction of symmetrical development in a double monster in as perfect 

 a manner as in a single and normal individual ; the two creatures 

 which, by their union, form either a partial or complete double mon- 

 strosity, are always joined by the homologous faces of their bodies — 

 side to side, front to front, or back to back. And not only are they 

 united by their homologous surfaces externally, but internally they are 

 allied by homologous organs : each part or viscus of one corresponding 

 to a similar part or viscus of the other ; so that each vessel, nerve, or 

 muscle on the plane of union of one, notwithstanding the apparent com- 

 plexity, is joined to the corresponding vessel, nerve, or nmscle of the 

 other : just as the two moieties of a single and central organ, originally 

 distinct and lateral, become naturally fused together at a certain period, 

 and in obedience to the laws controlling their formation and develop- 

 ment. A double monster is, therefore, only a being composed of four more 

 or less complete moieties instead of two, as in the single individual. 



"With regard to more complex monstrosities, we lind that, instead of 

 two moieties, as in the normal condition of an individual, or the four 

 moieties as in the double monstrosity, we may have six, eight, or even 

 more ; but yet the law of similar union prevails, and the moieties com- 

 bine in twos. Therefore it is that a triple monstrosity is only a double 

 monstrosity doubled, and a quadruple one a triple nionstrosity doubled 

 also — all the phenomena of the compound monstrosity being accounted 

 for on the same general principle. 



The formation of double monstrosities has given rise to some dis- 

 cussion, and at present there are two chief theories which are worthy 

 of notice. According to one of these, there have been originally two 

 ova, which may have been derived from one or from two Graafian 

 vesicles or follicles rupturing at the same, or nearly the same time, and, 

 passing down the oviduct together, towards the cornu, becoming fused by 

 pressure in their passage. The other theory supposes the existence of 

 only one ovum, by whose division or cleavage the double monstrosity is 

 formed. 



The first view is that which has found most favour, though recently 

 it has been considered as quite exploded by Dittmer,' who is in- 

 clined to adopt the latter theory, and believes that the double monster 

 is only an instance of bilateral symmetry carried too far. According 

 to him, in the primitive germ of the normal embryo a longitudinal 

 gi-oove is formed, which afterwards represents the middle line, the two 

 lateral parts developing symmetrically. But if this groove is too deep 

 at one or both ends, the two halves will there be separated ; and the 

 separated extremities have the power of producing the wanting lateral 

 * Rtichert and Du Bois-Rct/mond's Archiv, 1875. 



