identical, but it will be a gross abuse of such argument to therefore conclude that such minute differences of surroundings could account for one puppy being big and black, and another one small and brown in the same litter; or that one should resemble one parent, another the other, and a third a remote ancestor. It is, therefore, clear that _some at least_ of the variations in offspring are germinal or spontaneous in origin, and not in any way due to the environment of the embryo. The question remains whether all variations are due to this cause or whether some may be traced to environmental factors. One of the best lines of argument and investigation on this point is that of the bacteriologist, because microbes with which he is concerned may be regarded as equivalent in this matter to germ-cells, all microbes being unicellular. The problems of the germ-cell, and its heredity, therefore, are very similar in both cases. Tried by this test we may ask whether the changes produced in these unicellular organisms by the action of their environment are, or are not, inherited as variations. No one doubts for a single moment that a microbe as well as a germ-cell may be changed, or injured, or improved, according to its own special environment. What is in dispute is whether that change remains fixed in the succeeding generations to which these unicellular cells give rise. It is precisely here that the bacteriologist can offer evidence of a most important character. He will tell us that it is quite easy to change many of the characteristics of a microbe by altering its environment, which is undoubtedly true, but the further statement that they change because their germ-plasm is affected directly by the environment is not necessarily true. These organisms and germ-cells are composed of protoplasm whose ultimate constitution permits of their varying spontaneously. These variations are obviously to enable them to adapt themselves to the tissues of the animal in which they are living, and these variations also, or modifications as they really are, are usually lost when that environment is no longer existent. In other words they proceed no further than to allow the microbe to exist in a new environment. This seems to point undoubtedly to the fact that they are caused by selection of true variations. In other words what is ultimately produced is a condition of the germ-cell in which it becomes very highly resistant to any influence immediately exerted upon it by the environment, and so continues to live in successive generations without any further modification. The conclusion, therefore, is, in Dr. Reid's words, "that the germ-plasm is both spontaneously variable and highly resistant to the direct action of the environment. In other words we must believe that in any species that is not undergoing extinction spontaneous variations greatly preponderate over those which are caused by the direct action of the environment."