The number of malformations, however, to which this doctrine fully applies, is as yet very small. Amongst those which do not admit of such an explanation are duplicate formations, and the great majority of malformations designated by the term malposition.

(d.) The fourth proposition - which the countenance given to it by Wolff, by Tiedemann, and especially by J. F. Meckel, has caused to be the more generally received one - has formed the groundwork for an elaborate scientific inquiry into the subject, in especial connection with the history of development. This sets forth that most malformations represent certain stages of the development of the embryo and of its organs, at which stages formation has stopped short, or from which ulterior development has ceased to follow the normal type. The malformation is therefore essentially an arrest of development.

This theory of malformations is in a great measure correct. Still it does not attempt to explain the cause of the arrest, which may be one of those already enumerated, be it concerned with the germ, with sickening of the embryo, with mechanical influence, or with mental emotion.

A good classification of malformations is, owing to the difficulty of establishing a principle of division generally applicable, as yet wanting. If we attempt to classify them according to external form, we meet with a barrier in their multiplicity. Another obstacle consists in this, that where several malformations coexist in the same individual, they must needs all be classified according to the one most pronounced, and the designation be therefore partially incorrect. A classification founded upon the occasional causes is impracticable, since the same malformation may originate from various causes. If we take for the basis external form and cause conjointly, the classification becomes bereft of logical unity.

It is desirable that we should become acquainted with the principles upon which the more remarkable classifications hitherto propounded are built.

Passing over the older classifications, we should except that of Buffon, as it forms the groundwork upon which almost all the latter ones are modelled. Buffon divided malformations into three classes: 1, malformation with excess; 2, with deficiency; 3, with inversion or perverse site. To this classification we may subjoin that of Blumenbach, under the following four heads: 1, fabrica aliena; 2, situs mutatus; 3, mon-stra per excessum; 4, monstra per defectum. These were followed by Meckel in his division of malformations, as follows: 1, malformation from deficient plastic power; 2, from excess of plastic power; 3, from deviation of the organs in respect to their natural form; 4, malformations characterized by ambiguity of sex - hermaphroditism. This distinction of hermaphroditism from other malformations constitutes the great defect of Meckel's classification.

Breschet has, in his classification, broken up Buffon's first class into two, by separating duplicate formations from malformations per exces-sum. The four orders of his classification are: 1, ageneses, devious formations with diminution of plastic power; 2, hypergeneses, with augmentation of plastic power; 3, diplogeneses, devious formations with the fusion of germs - duplicate formations; 4, heterogeneses, with alien character of the product of generation. The further division is as follows:

The first order, ageneses, breaks up into four species.

(A.) Agenesie, Absence - Defective Development

It is either partial, as in hemicephalie, aprosopie, acephalie, apleurie; or it is general, as in microsomatie (dwarfishness, cretinism).

(B.) Diastematie, Cleft Formation At The Median Line

It is subdivided according as it affects the head or the trunk, into diastemence-phalie, etc, and diastematosternie, etc.

(c.) Atresie.

(D.) Symphysie, Coalition Fusion

The second order, hypergenese, presents two species, according as individual parts or the entire body are concerned. To the former species belong macrocephalie, macroprosopie, etc.; the latter consists of macro-somatie (giant growth).

The third order, diplogenese, is divisible into external, through fusion or adhesion, as in diplocephalie, diplothoracie; and internal, through penetration (per penetrationem).

The fourth order has three species.

(a.) Deviation as to site, either of the entire organism [extra-uterine pregnancy] or of individual organs [ectopie]. (b.) Deviation as to number, polypsedie - the coexistence in the uterus of several foetuses. (c.) Deviation as to color - leucopathie, cyanopathie, cirrhopathie.

In this arrangement, the distinction of dip-ogenesis from hypergenesis is based upon the unproved doctrine of the fusion of two germs constituting duplicate formation. To the order, heterogenesis, are referred deviations which ought not to be designated as malformations.

One of the best known classifications of late years is that of the two Geoffroy St. Hilaires, father and son, who handle malformations, according to the natural method, under the term teratology (from rspac, mon-strum).

Malformations are simple and complex - anomalies simples et complexes.

The simple - hemiteries - are either so-called variations, lusus naturae, where the anomaly is slight, causing neither disturbance of function nor deformity, or else defects of conformation, malformations in a restricted sense, where, however trifling the anatomical deviation, they impede or preclude the exercise of one or more functions, or occasion deformity.

They are divided into five classes, the anomaly being respectively concerned with:

1. Volume, as regards size, both of the body generally, and of its individual parts;

2. Form;

3. Structure and coloration;

4. Disposition;

5. Number and existence, that is absence or presence of parts.

These classes, according to extent and to degree - according to the kind of malformation, are divided into orders, and these again distinguished according to the regions, systems, and organs involved. Thus the first class comprises the four orders - general dwarfishness and general gigantism, partial gigantism and partial dwarfishness of proportions. The fourth class includes the five orders - displacement, preternatural union, preternatural connection, sept-formation, disjunction, etc.