414 



FCETAL DYSTOKIA. 



sion, 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, become 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 favor, though quite re- 

 cently it has been considered as quite exploded by Dittmer {Reichert and 

 Dii Bois-Reymond's Archiv., 1875), who is inclined to adopt the latter 

 theory, and believes that the double monster is only an instance of bi- 

 lateral symmetry carried too far. According to him, in the primitive 

 germ of the normal embryo a longitudinal groove is formed, which after- 

 wards represents the middle line, the two lateral parts developing sym- 

 metrically. 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 half of each. The separation of 

 the two halves may occur at one extremity or at both, and it may extend 

 to any depth. According to these differences, we should have the vari- 

 ous forms of double monster — from such creatures as the Siamese twins 

 to cases of a small supernumerary leg. There may even be a further 

 stage of this process. One of the separated halves may present a sim- 

 ilar exaggeration of bilateral symmetry, if it again separate into two 

 halves like the original germ. 



Thus may be explained monsters with three heads or three tails. 



Some objections might be raised to this theor}^ but this is not the place 

 to enter upon their discussion. We may, however, point out that it will 

 scarcely apply to included monstrosities, in which we have one creature, 

 more or less perfectly developed, contained within another. We can 

 scarcely doubt of the existence of two ova, the included one being the 

 oldest, and that this inclusion has probably been effected at a very early 

 period of germ development. 



To return, however, to the long-accepted theory. If we descend from 

 the complex phenomena of double monsters to single ones, and from 

 these to simple anomalies, we find again that every anomalous union be- 

 tween organs takes place by homologous parts. What have been desig- 

 nated " Symelian " monstrosities are characterized by the fusion of their 

 more or less atrophied abdominal limbs ; in the " Cyclocephalian " mon- 

 sters the eyes are more or less fused into one organ of vision ; while with 

 the " Otocephalians " the ears themselves are joined, and often inti- 

 mately confounded. The union of the kidneys, testicles, cerebral hemi- 

 spheres, and other double organs, is often observed in creatures otherwise 

 normal in conformation ; and all these anomalies occur under the reign 

 of the same law — that of " similar union " — which for organs, as for en- 

 tire individuals, operates on homologous parts. 



With regard to the remote or proximate causes which lead to the pro- 

 duction of monstrosities, it is very probable that the most prominent are 

 irregularity or inequality in the nutrition of the foetus, physical injury, 

 undue pressure, alterations in the membranes, or diseased conditions of 

 the young creature. G. Saint-Hilaire and Valentine, by disturbing the 

 development of the embryo of the fowl during the early stage of incuba- 

 tion of eggs — through shaking, jarring, and pressing them, perforating the 

 shell, or covering it with w^x — could almost create monstrosities at will. 



