individual characteristics. Hence the evident conclusion that heredity is the law, non-heredity the exception. Suppose a father and mother-both large, strong, healthy, active and intelligentproduce a son and a daughter possessing the opposite qualities. In this instance, wherein heredity seems completely set aside, it still holds good that the differences between parents and children are but slight, as compared with the resemblances.

Let it not be said that we have dwelt too long on points that are self-evident. They are so clear that we forget them, and argue only from isolated cases, thus changing the state of the question by the way in which it is stated. But when, on the contrary, wẹ consider the facts as a whole, heredity appears universal, and we are less surprised at finding characteristics that are hereditary, than in finding those which are not.

CHAPTER II.

THE LAWS OF HEREDITY.

THUS, then, heredity presents itself to us as a biological law, that is, inherent in every living thing, having no other limits than those of life itself. Life under all its forms-vegetal, animal and human, normal and morbid, physical and mental-is governed by this law. It is, in fact, concerned with the essential and inmost nature of vital activity. Among the various functions which in their united action constitute life, two are primary-the one, nutrition, which preserves the individual, the other, generation, which perpetuates the species. Some physiologists even reduce these to one, nutrition being, in their view, only a form of generation, or in the words of Claude Bernard, 'a continuous creation of organized matter by means of the histogenic processes appertaining to the living creature.' Ultimately, therefore, the vital functions are reduced to generation; and as it is from this that heredity immediately flows, we must conclude that the law of hereditary transmission has its rise in the sources of life itself.

If we accept the foregoing views, the law of heredity would seem to be one of absolute simplicity. Like produces like: the progenitor is repeated in the descendant. Thus the primitive types would

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remain, being continually reproduced, and the world of life would present the spectacle of perfect regularity and supreme monotony. But this is true only in theory. So soon as we come to the facts, we find the law is resolved into secondary laws, or it even appears to vanish in the exceptions. Not to speak of the external causes (chance, influence of circumstances) which interfere with the action of heredity, there are interior causes, inherent in heredity itself, which hinder the law from pursuing the simple course from like to like. A moment's reflection will make this plain.

In the inferior creatures, in which generation takes place without sexual connection, hereditary transmission from the parent to the progeny occurs in a perfectly natural way. This happens in cases of fission, as in Trembley's hydra, or in the Nais, which naturally divide into two or more individuals like themselves; and also in cases of gemmation, where a bud forms on an animal and is soon itself changed into a new and complete animal.

But in the higher forms of generation sexual connection is indispensable; as a struggle necessarily arises between the sexes, each parent tends to produce its like. Here hereditary transmission can at best produce only a mixed constitution, holding from both parents. 'Clearly,' says De Quatrefages, the mathematical law of heredity would be for the parent creature to reproduce itself completely in its progeny. And perhaps this law, absolute though it be, is to be found underlying all natural phenomena, but in every case it is masked by accessory circumstances, by the conditions amid which heredity acts. But it does not only rest on theoretical considerations, it rests also on facts. Although subject to profound and continual disturbance, still, if we note all the phenomena which show in individuals a tendency to obey the mathematical law, heredity is found to realize in the aggregate of each species the result which it fails to realize in isolated individuals. To use a figurative expression, the true meaning of which cannot fail to be apprehended, while it cannot be verified in the whole, it may be in detail.'

The question is still more complicated when we descend to individual facts. We meet with so many oddities and exceptions, and so many contradictory opinions in explanation of them, that it seems as though, when we pass from theory to practice, all law

had vanished. Still these facts, however numerous and varied they may be, may all be brought within the compass of a few formulas, which might be called the empirical laws of heredity. These real laws, which are so many aspects or incomplete expressions of the ideal law, are the following, so far as observation reveals them.

1. Direct heredity, which consists in the transmission of paternal and maternal qualities to the children. This form of heredity: offers two aspects:

(1.) The child takes after father and mother equally as regards both physical and moral characters, a case, strictly speaking, of very rare occurrence, for the very ideal of the law would then be realized.

Or (2), the child, while taking after both parents, more specially resembles one of them; and here again we must distinguish between two cases.

a. The first of these is when the heredity takes place in the same sex-from father to son, from mother to daughter.

B. The other, which occurs more frequently, is where heredity occurs between different sexes-from father to daughter, from mother to son.

2. Reversional Heredity, or atavism, consists in the reproduction in the descendants of the moral or physical qualities of their ancestors. It occurs frequently between grandfather and grandson, grandmother and granddaughter.

3. Collateral, or indirect heredity, which is of rarer occurrence than the foregoing, subsists, as indicated by its name, between individuals and their ancestors in the indirect line-uncle, or grand-uncle and nephew, aunt and niece.

4. Finally, to complete the classification, we must mention the heredity of influence, very rare from the physiological point of view, and of which probably no single instance is proved in the moral order. It consists in the reproduction in the children by a second marriage of some peculiarity belonging to a former spouse.

Such are the various formulas under which all the facts of heredity may be classed. We propose to study them in succession. When to this we have added, as the necessary complement, the study of the exceptions to these laws, we shall have passed in review every single case of heredity.

SECTION 1.-DIRECT HEREDITY.

I.

We have first to resort to physiology in order to clear the field, since the laws of physiological heredity have been oftener and far better studied than those of moral heredity; yet so close is the connection between the two orders of facts, that a person can hardly study the one without the other.

In the case of direct heredity, the concurrence of the two sexes in the formation of the product is now admitted by all physiologists. We need, therefore, only refer to the ancient doctrines of the spermatists and the ovists. The former held that, notwithstanding the apparent concurrence of both sexes in generation, the germ is contained in the male element alone. The latter, who held a doctrine the very reverse of this, but equally exclusive, maintained that the germ exists only in the female element. The first doctrine, which was adopted by Galen, Hartsoeker, Boerhaave, Leeuwenhoek, and the second, which was held by Malpighi, Vallisnieri, Spallanzani, Bonnet, Haller, and even De Blainville, are now equally abandoned. It is admitted that the child is sprung from both father and mother, and embryology demonstrates this. But opinions diverge in regard to the part taken by each of the parents.

If we take a purely theoretic point of view, it is easy enough to formulate the law of direct heredity. According to P. Lucas, it would consist in the absolute equilibrium in the physical and moral nature of the infant of the integral resemblances of the two parents.' The procreated individual would be, everywhere and always, nothing but the exact mean of his two parents; the distinct characters of both would be reproduced in their progenyin every portion of his body, and in every faculty of his mind. But this is only a logical hypothesis, which very rarely becomes a reality in the higher animals; and it is hardly rash to say that the law has never been met with in this ideal form.

And yet we understand that this is the law, that is to say, the only formula broad enough to include all the phenomena; the only rule which flows of necessity from the nature of things, and which expresses the essence of heredity.

It is easy to account for the disagreement between logic and experience. No law of nature is unconditional. They all require certain determinate conditions for their realization; and where these fail, the action of the law rests suspended, or without efficacy. But nowhere are the requisite conditions more numerous or more difficult to fulfil than in the phenomena of generation. For in order to produce in the infant this perfect equilibrium of paternal and maternal qualities, there must evidently be perfect equality of action on the part of both parents; for it will be admitted that in all races, and in all species, the general or partial preponderance in the act of reproduction appertains to that one of the parents in whom the general or partial force of constitution is the greater. A great number of facts, collected by a crowd of writers, show that this rule applies both to the vegetal and the animal world. This preponderance of one of the procreative individuals is very notable in crosses between distinct races or species. It is true that in this case there is a struggle not only between the sexes, but between distinct specific forces. These crosses, however, only exhibit to us, more or less magnified, what takes place in ordinary cases. According to Rursh, marriages between Danes and East Indian women produce children with the physique and the vigour of the European type, while nothing of this kind occurs when these same women marry other Europeans. The intermarriage of Causasians and Mongolians produces, according to Klaproth, half-breeds in whom the Mongolian type is always predominant, whatever may be the sex of the half-breed. From Levaillant's observations (Voyage en Cafrérie) on the half-bred children of Europeans and Hottentots, we gather that in them the moral nature is always determined by the race of the father. 'Whenever it happens, which is but rarely, that a white woman has intercourse with a Hottentot, the child has always the good-nature, and the gentle and kindly inclinations, of the father. But the children of white men and Hottentot women, on the other hand, have in themselves the germs of all vices and unruly passions.' Cross breeding in the animal races exhibits also the unquestionable preponderance of one of the parents.

This being admitted, it may be readily shown that among the higher animals the complete conditions necessary for the realization of the ideal law can nowhere be found.