Enough has been said here by way of defining the terms of the issue. The negative we have to sustain is that the following facts and observations declare that certain small modifications cannot be governed by selection and are not correlated with useful characters. It will be shown later that Professor Thomson’s stringent condition is not in all of them compiled with, but that, in spite of this, the probability of their being valid examples of Lamarckism in practice is immense. CHAPTER IV. INITIAL VARIATIONS AND TOTAL EXPERIENCE. The present chapter is on _a priori_ lines and will perhaps be dismissed with a wave of the hand or hurriedly skimmed over, but I pray the reader at least to read the two or three last pages of it. It is at any rate suggestive, and perhaps I may anticipate the comments of the neo-Darwinian and throw myself on his mercy by mentioning a remark of the late Sir Andrew Clark, prince of physicians and genial cynic, which he made to a patient in my presence. A lady not distinguished for depth of thought asked him a rather silly question in medicine. As if offended he drew himself up, holding in his hand a cup of tea which he was enjoying, and replied at once “Madam, you must get a younger and more inexperienced man than I am to answer you that question.” A very high degree of probability may be attached to the presupposition that Lamarckian factors, even in their humblest form, may enter into the story of the organisms as historical and living beings. Every hypothesis in matters of science, or, to put it at its lowest, every scientific guess must transcend the evidence at the time available. Total Experience.