So far I have spoken of heredity as though that term had become synonymous with Mendelian heredity. Those of as who are at work on Mendelian inheritance are often criticized as too narrow. It is said that we do not recognize that any other kind of inheritance takes place. I do not think the criticism is quite fair, because, in the first place, the very great number of variations studied has been shown to conform to the Mendelian principles or at least to be capable of such interpretation. There are, however, a few exceptional cases. In certain albino plants it has been shown that the inheritance of albinism can be traced to the behavior of the chlorophyll bodies in the cytoplasm. The chlorophyll bodies are known to divide and to be distributed to the two daughter cells at each division independently of the nuclear division and of the maturation process in the egg. Why, then, it is asked, may not there be present in the cytoplasm of the cell other self-perpetuating bodies that are responsible for certain kinds of inheritance? Why not go further and ask, why, since the cytoplasm appears to be handed down from cell to cell, may it not furnish also a different medium for inheritance of characters? Theoretically such an argument is logical. No student of Mendelism would I think deny such a possibility. But, as a matter of fact, it is not going too far to say that, at present, there is little evidence that such inheritance takes place, except in a few special cases, like that of the chlorophyll bodies. It is safe, I think, to say that if cytoplasmic inheritance played any important rôle in heredity in the higher animals and plants, we should expect, by now, to have found many cases of it. None are known to us. Whether Mendel’s laws of heredity apply to unicellular animals, to bacteria and to similar types, in which the mechanism for this type of inheritance has not been shown to exist, can not be affirmed or denied from the evidence at hand. There are at present three outstanding cases in the higher animals, in which an induced variation is said to be inherited afterwards. These cases are of great interest to pathology. We can not afford to pass them over. First, there is Brown-Sequard’s claim that injuries to the nerve cord or to the cervical or sciatic nerves of guinea pigs produce effects that are transmitted. Second, there are the cases of the inherited effects caused by alcohol in guinea pigs discovered by Stockard. Third, there is Guyer’s evidence that an effect on the eye, caused by foreign serum, is transmitted. Brown-Sequard’s experiments have been repeated several times; almost always with negative results. Today his claims are practically forgotten.