itself, but are simply the result of abnormal stimuli. Such modifications, no matter in what direction they may be, are, of course, not transmissible to the next generation, for the very obvious reason that the germ-cells which are to be concerned with the next generation have been already produced. The germ-plasm itself passes on unchanged in so far as its hereditary possibilities are concerned. We see, therefore, that in order to think clearly on this matter we must limit the meaning of the word variation to such differences or changes in germ-plasm which indicates some real change of an inheritable nature. The term should not be used to apply to a mere passing environment, in which the germ-plasm happens to be, caused by the presence of poisons, or similar factors.

Given then the fact that variations do constantly and inevitably occur in offspring owing to new qualities arising in germ-plasm itself, it is obvious that these variations are either what are termed “spontaneous,” or else they must be due to the action of the surroundings on the germ-plasm. By the term “spontaneous,” in this connection, it is not meant that these variations arise without cause or in a haphazard manner. It is simply meant to imply that the present state of our knowledge does not justify us in stating what does actually cause the variation in germ-plasm, or the laws in accordance with which such variations occur. That they must be a matter of cause and effect and law every biologist believes, but until the law can be demonstrated, the term “spontaneous” may well be retained to distinguish these variations from those which arise by the obvious action of environment. For example, the variations which occur as the results of reproduction from two parents, do so because of the mingling of the respective germ-cells, and such variations come under the group of “spontaneous”; whereas changes induced on account of the food supplied, or poisonous substances in fluids surrounding germ-cells are not spontaneous, but environmental.

A point of great interest to the embryologists is the question whether the differences of detail which exist between children and their parents are of the nature of spontaneous variations, taking their origin in the germ-plasm itself, or mere modifications produced by the action of the environment of the embryo. Further, should both these factors play a part in producing these differences, which is of greater importance, and in what proportion? This question is elaborated in great detail by Dr. Archdall Reid, in his work, The Laws of Heredity, which ought to be read by every intelligent citizen and parent who is interested in the welfare of the young. In the main in this subject we follow the ideas so ably put forward by him. He points out that the offspring of the same parents always differ not only from the parents, but among themselves, even if they be twins, and amongst the lower animals every member of a litter of dogs, or pigs, or kittens, shows differences in size, colour, activities, temperament, and characteristics. Are those differences due to the action of environment on the embryo or do they take their origin in the germ-cells from which the individuals came? Inasmuch as a litter of puppies is subjected to precisely the same environment during the whole time of development, it is perfectly obvious that such differences as they exhibit at the time of birth must have been germinal, an identical environment could not by any stretch of the imagination be held responsible for producing variations. They, therefore, must be of the spontaneous variety. Of course it may be argued that even during development the environment of each embryo within the mother is not 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.”

This quality of single cells, that is to say of the germ-plasm of all species which continue to exist, in virtue of which it resists very strongly any efforts to change it, is a very important matter to grasp. Without it it is quite obvious that no species could maintain its characteristic features for any length of time. Were it not for this resistant power, germ-plasm would be easily destroyed or continually and readily changed. The descendants from such continually changing germ-plasm would themselves be of such infinite variety that there would be no such thing as a definite species, so that there is no doubt whatever that germ-plasm has become, probably by the action of natural selection, extremely resistant to all influences of an environmental character.

That does not mean, of course, that germ-plasm cannot be damaged, or weakened, or changed in its tendencies. It does mean that when it is so changed it is principally as the result of injury, which may be indeed so severe as to destroy the germ-plasm itself. It would seem as if the inherited tendencies of germ-cells were so intimately bound up in the constitution of those cells as to be almost a matter of life and