(4) The reappearance of a modification may be mistaken for the transmission of a modification. Thus a blond European family moves to the tropics, and the parents become tanned. The children who grow up under the tropical sun are tanned from infancy; and after the grandchildren or great-grandchildren appear, brown from childhood, some one points to the case as an instance of permanent modification of skin-color. But of course the children at the time of birth are as white as their distant cousins in Europe, and if taken back to the North to be brought up, would be no darker than their kinsmen who had never been in the tropics. Such "evidence" has often been brought forward by careless observers, but can deceive no one who inquires carefully into the facts. (5) In the case of diseases, re-infection is often mistaken for transmission. The father had pneumonia; the son later developed it; ergo, he must have inherited it. What evidence is there that the son in this case did not get it from an entirely different source? Medical literature is heavily burdened with such spurious evidence. (6) Changes in the germ-cells _along with_ changes in the body are not relevant to this discussion. The mother's body, for example, is poisoned with alcohol, which is present in large quantities in the blood and therefore might affect the germ-cells directly. If the children subsequently born are consistently defective it is not an inheritance of a body character but the result of a direct modification of the germ-plasm. The inheritance of an acquired modification of the body can only be proved if some particular change made in the parent is inherited as such by the child. (7) There is often a failure to distinguish between the possible inheritance of a particular modification, and the possible inheritance of indirect results of that modification, or of changes correlated with it. This is a nice but crucial point on which most popular writers are confused. Let us examine it through a hypothetical case. A woman, not herself strong, bears a child that is weak. The woman then goes in for athletics, in order better to fit herself for motherhood; she specializes on tennis. After a few years she bears another child, which is much stronger and better developed than the first. "Look," some one will say, "how the mother has transmitted her acquirement to her offspring." We grant that her improved general health will probably result in a child that is better nourished than the first; but that is a very different thing from heredity. If, however, the mother had played tennis until her right arm was over-developed, and her spine bent; if these characteristics were nowhere present in the ancestry and not seen in the first child; but if the second child were born with a bent spine and a right arm of exaggerated musculature, we would be willing to consider the case on the basis of the inheritance of an acquired character. We are not likely to have such a case presented to us.