as a rule-but that direct steps from species to species have been made.

Nor is such a method of evolution inexplicable. In fact, Darwin has, perhaps, unnecessarily limited the application of his own principles, in confining the molding influences to minute variations. We know that there are many variations which are far from being minute. Extreme variations are occasionally produced, and marked variations which are capable of hereditary transmission are not uncommon.

The minute variations considered in the Darwinian theory are of universal occurrence. Perhaps no case ever arises of a completely normal birth-of an offspring precisely intermediate in all respects between its parents. Variations in size and vigor of the body as a whole, of the separate organs of the body, of the tissues composing these organs, &c., never fail to occur. There is a constant tendency to deviate from the type. And this tendency is in continual conflict with the opposite tendency produced by the struggle for existence and the necessity of preserving the best adaptation to natural conditions.

These minor variations may be due to variations in polar vigor of the molecules. We have already considered the question of molecular energy, and ascribed it to the degree of chemical polarity. The most vigorously acid or basic molecules must have the most vigorous growth energy. But this chemical polarity is constantly affected by cell division. The cells arising from continued division of a primary cell must differ widely in polarity, ranging from the neutral to the extreme of acid or basic conditions. Perhaps the free buds of the tissue cells may be their most vigorously polar offspring, yet differences cannot but occur in their degree of polarity, and the germinal cell into which they aggregate is perhaps made up of molecules considerably differing in chemical activity. In its evolution the growth vigor of the new tissues must be controlled by the chemical energy of the molecules from which they arise. Hence there may be variations from the parental form in every tissue and organ of the new form. The union of germs of two individuals adds a new element of complication to the case. If the molecules of the bisexual germs constitute poles of a galvanic circuit, there may be as many diverse circuits as there are diverse sets of molecules, and the chemical energy of each circuit will be controlled by the

chemical vigor of its weaker pole. In developing there is a tendency to reproduce a normal copy of one parent in one lateral half of the offspring, and the other parent in the other half. But this tendency is checked by the influence exerted by each pole of the germ upon the other, so that the two halves of the body are forced into close though not into exact accordance. Chemical vigor of the molecules must give special nutritive vigor to the tissues arising from them, and it may also yield a tendency to increased cellular coherence, thus doubly aiding the growth vigor of these tissues, while the weaker tissues may be more inclined to bud off free cells from lack of local nutrition.

It is possible that we have in this diversity of molecular chemical activity in the germ an explanation of the marked physical diversities in the tissues thence arising. But there are many cases of abnormal birth which cannot be ascribed to this cause. These abnormalities are very numerous, and differ widely in degree, but may be all grouped under three classes. In one class there is a deficiency in one or more tissues; in another class there is an excess; in a third class the tissues are normal but are displaced. In all these classes the normal type of the body is distinctly departed from.

Surgical records give abundant cases in each of these classes of anomalies. In the first class are deficiencies of every degree, from a very slight lack of tissue to an extreme deficiency. In some cases the limbs are missing, in some the head, in some the brain, in others parts of the viscera. Here a mere trunk appears without head or limbs. In the extreme case a mere shapeless lump of flesh is produced, destitute of any organic differentiation. A frequent case of deficiency is a lack of tissue in the line of junction of the lateral halves of the body. This causes coalescoalesce, in some the

cence of organs. In some cases the eyes sides of the nose, in some the jaws, this being sometimes so extreme that the ears are united into one. Similar cases of coalescence occur in the viscera, and in the lower limbs, which unite into one.

The second class of anomalies, that of excess organs, is equally marked. In a not unusual case an extra finger appears on each hand, often accompanied by an extra toe on each foot. From this simple duplication there are cases leading up to the most extreme duplication. Three or four eyes, a double tongue, heart,

brain, face, and so on, appear, until every organ is duplicated. In more extreme cases we have duplication of the lower limbs, a double head, the head and part of the trunk double, and finally the whole body double, the two halves being united either intimately or by only a slight bond, like that of the Siamese twins. In some cases a triple body has appeared. These twin formations are not the result of a chance union of developing germs, for a complete series of duplications, from the slightest to the most extreme, are upon record.

Another set of anomalies, that of cleft or division between the lateral halves of the body, may perhaps be included in the same class. An ordinary case of this kind is that of cleft or hare lip, but it is found in every part of the dividing line of the body. The two sexual halves seem to have a tendency to develop separately, and this is perhaps a step in the process of duplica

tion.

The third class of anomalies alluded to is that of displacement of organs. This also is of frequent occurrence. A few instances will suffice for illustration. The twin internal organs, the two kidneys, for instance, sometimes occur on the same side of the body. Of the exterior organs, a case is on record in which the thumb was missing on one hand, while a double thumb appeared on the other. A more striking case is one in which one foot had but a single toe, while the other foot had eight, one of these being partly cleft in indication of the ninth. Another case is that of eleven ribs on one side and thirteen on the other.

These anomalous births may have far more importance than has been ascribed to them; possibly, indeed, they may be of essential significance in the question of the origin of species. But before considering their consequences, it may be well to consider their cause. In doing so it becomes necessary to carry the theory of the struggle for existence further back than is usually done. Ordinarily it is made to apply only to the case of survival of the fittest in mature forms or in well developed embryos. But it may be applied with equal justice to the struggle for existence between germs, or between the leucocytes of the blood. These self-feeding amoeboid corpuscles battle for nutriment. It is not probable that they all become fully generalized. Those most fully generalized possess the best nutrient relations to the blood, and are most apt to survive. Those only partly generalized are

apt to lose their vitality and become nutriment for more vigorous leucocytes, or for the body tissues.

But many imperfectly developed leucocytes may be excreted by the reproductive glands and pass into the ovaries or the testes. Here a new struggle for existence arises, in which the best developed germs are undoubtedly favored, but in which chance circumstances may give an imperfectly developed one an advantage in the struggle. Where the lack of normality is slight, the chances for development are nearly equal. Where it is great, only abnormal conditions in the reproductive organs can give the abnormal germ the advantage; consequently the production of a considerable anomaly is of rare occurrence.

It is probable that cases of reversion to ancestral types are instances of germinal deficiency. The embryo, in its development, seems to pass through phases resembling every ancestral type of the species, and a partial deficiency of molecular organization in the germ may limit the development of some organ or tissue. at the point reached by a more or less remote ancestor. Frequently there are reproduced characteristics of an ancestor a few generations removed. Occasionally there may be of a very remote ancestor. The sexual union of a normal with a deficient germ cannot yield a normal offspring, since the opposite polarities necessary to normal development are only partially present. For this reason every anomaly crosses the lateral line of the body, since the molecules of neither sexual side can develop without aid from those of the other.

As for the anomaly of displacement of organs, its cause is not apparent. The mode of arrangement of the germinal molecules controls the direction of their development, and the normal arrangement is forcibly produced through the action of the special polarities of these molecules. Yet perhaps there is some slight possibility of variation in the position of the molecules in the germ. If so, an exceedingly slight molecular displacement might produce a strongly marked organic displacement in the developed body.

The third class of anomalies, that of duplication, can also be met by a conjectural explanation. It may arise from duplication of leucocytes in the glands; two leucocytes coming from the same region of the body, and passing through the same lymphatic gland, may possibly combine, and thus yield a doubly

polar corpuscle. If so, the germ thence arising would have a double, or perhaps a triple polarity in some of its molecules. And this duplication will be more complete as the gland producing it is a more central one. It may vary from the production of a slight duplication of tissue to that of a combination of two fully generalized leucocytes. If such a germ, with part or all of its molecules doubly polar, combine with a germ of the opposite sex and develop, the bisexual germ thus produced would be, to some extent, bipolar at one sexual pole and unipolar at the other. But as each pole exerts a controlling influence upon the development of the other, the result might be a bipolar or a unipolar organism, as one or the other sexual pole was preponderant in

energy.

If duplication of organs or of bodies has its origin in the action of the glands upon the development of the leucocytes, as here supposed, this must, in some cases at least, result from abnormal organization of the glands. Only thus can be understood the frequent recurrence of the same malformation out of the same parents; this extending to the extreme case of twin births, which may occur more than once from the same mother.

Having thus offered some conjectural explanations as to the physiological cause of abnormal births, it remains to consider their bearing upon the question of the origin of species.

Abnormal offspring do not succumb without a struggle for life. Twin monstrosities often survive to maturity. A deficiency so extreme as the total lack of a brain does not cause immediate death. Brainless children have survived for some time after birth. Of course the chances are enormously against extreme aberrations from the normal type being transmitted. But slight aberrations are sometimes stubbornly transmitted, particularly if they be such as do not specially affect the life chance of the individual. Thus an extra finger may be sent down through several generations, and undoubtedly could, by intelligent sexual selection, be made a type feature. It stubbornly resists reversion through the influence of union of the abnormal with a normal individual.

There is a race prejudice which operates against the transmission of external abnormalities, but which cannot affect that of internal ones. The duplication of a muscle, for instance, would not appear externally, yet might give the animal possessing it some