Such in fact is the case; for we know, it may fairly be said, nothing about the vehicle. There are two very widely distinct opinions on this point. There is the mnemic theory, recently brought before us by the republication of Butler's most interesting and suggestive work with its translations of Hering's original paper and Von Hartmann's discourse and its very illuminating introduction by Professor Hartog.[5] And there is the continuity theory which teaches that in some way or another the characteristics of the parents and other ancestors are physical parts of the germ. An attempt to explain this was made by Darwin in his theory of Pangenesis. Others have essayed what Yves Delage calls "micromeristic" interpretations. As to all of these it may be said that when they are reduced to figures the explanation becomes of so complex a character as utterly to break down. We shall see that Professor Bateson adopts a third very nebulous explanation. But as regards the laws of heredity there is something else to be said; for here we really do know something, and that something we owe in large measure to the innumerable experiments which have been made on Mendelian lines since the re-discovery of the methods first adopted by the celebrated Abbot of Bruenn. It is no intention of the writer of this paper to describe the Mendelian theory,[6] which is well known, at least to all biological readers, though one or two points in connection with it may yet have to be touched upon. The point of cardinal importance in connection with Mendelism is that it does reveal a law capable of being numerically stated, and apparently applicable to a large number of isolated factors in living things. Indeed it was this attention to isolated factors which was the first and essential part of Mendel's method. For example, others had been content to look at the pea as a whole. Mendel applied his analytic method to such things as the colour of the pea, the smooth or wrinkled character of the skin which covered it, its dwarfness or height, and so on. Now, the behaviour of these isolated factors seems to throw a light even upon the vehicle of heredity. We often talk of "blood" and "mixing of blood," as if blood had anything to do with the question, when really the Biblical expression "the seed of Abraham" is much more to the point. For it is in the seed that these factors must be, whether they be mnemic or physical. Professor Bateson (M., p. 5) thinks it obvious that they are transmitted by the spermatozoon and the ovum; but it seems to him "unlikely that they are in any simple or literal sense material particles." And he goes on to say, and this, I think, is one of his most important statements: "I suspect rather that their properties depend on some phenomenon of arrangement."