the theory itself, but point it out simply as one of the consequences of the theory.

It has been shown quite recently, by Charrin, Delamare, and Moussu, that when, after the operation of laparotomy on a pregnant rabbit or guinea-pig, the kidney or the liver has become diseased, the offspring sometimes show similar affections in the corresponding organs (kidney or liver). The result is due, the authors think, to some substance set free from the diseased kidney of the parent that affects the kidney of the young in the uterus. By injecting into the blood of a pregnant animal fresh extracts from the kidney of another animal, the authors believe that the kidney of the young are also affected. It will be observed that this transmission of an acquired character appears to be different from that of transmission through the egg; for it is the developing, or developed organ itself, that is acted upon. The results throw an interesting light on the cases of epilepsy described by Brown-Séquard, since they show that the diseased condition of the parent may be transmitted to the later embryonic stages. May not, therefore, Brown-Séquard's results be also explained as due to direct transmission from the organs of the parent to the similar organs of the young in the uterus?

There is another series of experiments of a different sort that has been used as an argument in favor of the Lamarckian view. These are the results that Cunningham has obtained on young flatfish. He put the very young fish, while still bilaterally symmetrical (in which stage the pigment is equally developed on both sides of the body) into aquaria lighted from below. He found that when the young fish begins to undergo its metamorphosis, the pigment gradually disappears on one side, as it would have done under normal conditions, i.e. when they are lighted from above. If, however, the fish are kept for some time longer, lighted from below, the pigment begins to come back again. "The first fact proves that the disappearance of the pigment-cells from

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Parentson a from the over nde trogom les fue to sewa sa qet does not act upon that nde for vien is 4.08% %% as pigmentseva appar It seems to me that jamale sono ion from these facts is that the 4 vasgeant of pigmentosa va orignally due to the wwerte de tiers and that the change has now become The pigmentcella produced by the action of »Z** C**** Zower vide are in all respects similar to those Boraj prenent on the upper side of the fit. If the disappearance of the pigmentcells were due entirely to a wanation of the germ-plaam, no external influence could raise them to rappear, and, on the other hand, if there were no hereditary tendency, the coloration of the lower side of the fatfish when exposed would be rapid and complete."

This evidence might be convincing were it not weakened by two or three assumptions. In the first place, it is not shown that if the loss of color on the lower side had been the result of the inheritance of an acquired character that the results seen in Cunningham's experiment would follow as a consequence. Thus one of the starting-points of the argument really begs the whole question. In the second place, it is unproven that, had the loss of color of the lower side been the result of a variation of the germ-plasm, no external influence could cause it to reappear. In this connection there is another fact that has a bearing on the point here raised. In some species of flatfish the right side is turned down, and in other species the left. Occasionally an individual is found in a right sided species that is left-sided, and in such cases the color is also reversed. Now, to explain this A Natural Science, October, 1893.

in the way suggested by Cunningham, we should be obliged to assume that some of the ancestors acquired the loss of pigment on one side of the body, and others on the other side according to which side was turned down. This supposition might be appealed to to give us an explanation of the occasional reversal of the symmetry as a rare occurrence at the present time; but the argument is so transparently improbable that, I believe, the Lamarckian school would hesitate to make use of it, yet, in principle, it is about the same as that Cunningham has followed above.

If, on the other hand, we suppose the difference in color of the two sides to have been the result of a germ-variation, we need only suppose that this was of such a kind that the color of the under side is only in a latent condition, and if an external factor can cause a reaction to take place on the light side, it is not surprising that this should call forth the latent color patterns. The result can be given at least a formal explanation on the theory that the original change was a germ-variation.

We come now to the evidence derived from paleontology. A number of evolutionists, more especially of the American school, have tried to show that the evolution of a number of groups can best be accounted for on the theory of the inheritance of acquired characters. A point that we must always bear in mind is that evolution in a direct line need not necessarily be the outcome of Lamarckian factors. Some of our leading paleontologists, Cope, Hyatt, Scott, Osborn, have been strongly impressed by the paleontological evidence in favor of the view that evolution has often been in direct lines; and some, at least, of these investigators have been led to conclude that only the Lamarckian factor of the inheritance of acquired characters can give a sufficient explanation of the facts. Paleontologists have been much impressed by the fact that evolution has been along the lines which we might imagine that it would follow if the effects of use and

1 tisuse are inherited There is, however, 10 prief that this is the case though there are a number of nstances which this mode of explanation perse the racest soution. But as has been said her Is this kind of evidence that the theory is in need of since Lamarck himself gave an ample supply of lustrations. What we need is clear endence that this sort of intertance is possible. nd. from the very nature of the case. I is not ins endence that fossil remains can never supply.

The same criticism may be made of the work of Ryder. Packard, Dall Jackson. Eimer. Cunningham, Semper. De Vangry, and others of the Lamarckian sencel Despite the large number of cases that they have collected, which appear to them to be most easily explained on the assumption of the inheritance of acquired characters, the proof that such inneritance is possible is not forthcoming. Why not then spend a small part of the energy, that has been used to expound the theory, in demonstrating that such a thing is really possible? One of the chief virtues of the Lamarckian theory is that it is capable of experimental verification or contradiction, and who can be expected to furnish such proof if not the Neo Lamarckians?

We may fairly sum up our position in regard to the theory of the inheritance of acquired characters in the verdict of "not proven." I am not sure that we should not be justified at present in claiming that the theory is unnecessary and even improbable.

CHAPTER VIII

CONTINUOUS AND DISCONTINUOUS VARIATION AND HEREDITY

THE two terms continuous and discontinuous variation refer to the succession or inheritance of the variations rather than to the actual conditions amongst a group of individuals living at the same time; but this distinction has only a subordinate value. The term fluctuating, or individual variation, expresses more nearly the conditions of the individuals of a species at any one time, and the continuation of this sort of difference is the continuous variation spoken of above. The discontinuous variations are probably of the same nature as those that have been called mutations, and what Darwin sometimes called sports, or single variations, or definite variations.

CONTINUOUS VARIATION

If we examine a number of individuals of the same species, we find that no two of them are exactly alike in all particulars. If, however, we arrange them according to some one character, for example, according to the height, we find that there is a gradation more or less perfect from one end of the series to the other. Thus, if we were to take at random a hundred men, and stand them in line arranged according to their height, the tops of their heads, if joined, would form a nearly continuous line; the line will, of course, incline downward from the tallest to the shortest man. This illustrates individual variation. An arrangement of this kind fails to bring out one of the most important facts connected with individual differences.