GENERAL CONSIDERATIONS BEARING ON THE GENESIS OF ANOMALIES.
Before the establishment of embryology on the basis of a science, the grave anomalies in development met with, and the cause of which could not be determined, were attributed to the will of the Almighty. Such in olden time was the established and not so unnatural belief in regard to the legendary Janus, Cyclops, Sirens, Chimeras, Centaurs, etc. This period of fable extended into the middle ages, and it was not until the XVIIth century that teratology began to be studied and to be understood.
The various views in regard to the genesis of animals which have been held since the discovery of the microscope are most curious. For in stance, Aromatari believed that the ovum contained the embryo already formed even before it had begun to develop; Swammerdam said that " in nature there is no such thing as generation, but only propagation, growth of parts and exclusion of all chance. Thus may be explained original sin, for all men who have since lived were contained in the beginning in Adam and Eve. When these germs are exhausted, the human race will cease to exist." This doctrine of the pre-existence of germs lasted into the XVIIIth century and was advocated by Malpighi. It was not till the time of Wollf, who showed that primitively the ovule does not contain the embryo, that it was overthrown.
Etienne and Geoffrey Saint-Hilaire, followed later by Dareste, first proved conclusively that all fecundated ovules are identical at the outset, and that some external cause, by interfering with their development, may determine the appearance of anomalies. Dareste in more than 9,000 experiments was able to produce all the types of monstrosities from the eggs of the chick, and thus showed that physical external causes could modify the evolution of the fecundated germ. Whilst then it may be considered as proved that external causes influence the production of monstrosities, it is also true that other factors are powerful in the same direction, and certain ones must, in a measure, act by modifying the male or the female ovule before fecundation. How could we explain, else, those malformations which are hereditary in certain families ? We would add that the influence of maternal impressions is very problematical, especially when we remember that exactly similar anomalies have been met with in certain animals in whom there can hardly be question of imagina tion.
[In reference to this point we would refer to the forthcoming volume (XI.) of the Trans. Am. Gyn. Society, where Fordyce .Barker maintains, • in a paper on " The Influence of Maternal Impressions on the Foetus," that the weight of authority must be conceded to be in favor of the doctrine that maternal impressions may affect the development, form and character of the foetus. In the discussion of this paper, Goodell related a remarkable case of the kind. There can be no question, we think, that there must exist some causal relation, although it is one of those hidden mysteries likely ever to remain beyond human ken.—Ed.] The varied causes of anomalies acthy producing: 1. Arrest of development; 2. Fusion of organs normally distinct. Genesis of Anomalies by Arrest of Development.—These may be grouped as under: A. An organ may not be formed at all, there being complete arrest in development. Aceplialic foetuses, absence of uterus or ovaries, etc.
B. An organ before attaining its definitive form stops short in a less advanced developmental phase. Bifid uterus or vagina.
C. Certain organs normally only exist during intrauterine life. These may persist after birth.
D. Adhesions may form between the embryo and the membranes or between parts of the foetus itself.
E. Anomalies may be consecutive to changes in the vascular or in the nervous system.
Genesis of Anomalies by Fusion.—These result, in general, from the fusion of two blastemas which should remain separate. Usually homolo gous parts unite. It seems as though the mid-portion of the body had disappeared, and the right portion had sunk into the left. When two homologous blastemas fuse, the result is symmetry in formation, and vice versd.
In the following table are classified the simple anomalies (hemiteric) which may affect the foetus. Detailed study of all is impossible. Certain of the more important we have already referred to Many of these simple anomalies are treated of at length in treatises on surgery, and therefore we will not describe them here. Of the remainder the essential ones have already been noted by us in other portions of this work. We pass at once to a brief study of heterotaxy, or inversion of the viscera, and to hermaphroditism.