life, their different and opposing forms of diet for their minds and bodies (I know which of the two diets of those men I would choose and with which of them I would prefer to be cast on a desert island) one can only say that the total experience of Mr. Chesterton differs from that of Mr. Shaw as cheese from chalk, which things, incidentally, are an allegory in the philosophy of life. [36] _Op. cit._ p. 6. [37] p. 5. The thought here briefly expressed falls well into line with Prof. Bateson’s statement that the directing cause of the environment is essential to the theory of Lamarck, and I do not hesitate to add to it the assertion that _all environment_, in the wide sense of total experience, _is discontinuous_. There are no such phenomena in total experience as unit-characters of allied forms, small variations are the rule. Without doubt a large proportion of the stimuli received by an organism are as figures written on a slate and at once wiped off. They are as the snows of yester year. The most they do is to contribute in their measure to the metabolism of the organism, being too numerous and minute to affect any structural change. In a higher form of life none but those which are frequently repeated in the individual and in succeeding generations can effect any structural response. Mould and Sieve. It will be remembered that a single example was given of a short-haired dog in which its common habit of lying was associated with a certain pattern of hair. This introduces and illustrates the very wide conception of a moulding process undergone by an organism. It is one familiar to biologists and very much so to Professor Thomson in his various writings. Not less is he an exponent of the metaphorical work of the sieve of natural selection. I therefore claim nothing new when, with the temerity of certain persons treading where others are said to fear to do so, I invent an inclusive term and propose to call the two fundamental factors of organic evolution _Plasto-diēthēsis_[38] in which the conceptions of mould and sieve are included and hyphenated. This word is no more proposed for its elegance than are _panmixia_, _amphimixis_ and _tetraplasty_, though perhaps it may be the etymological superior of one or more of these. It is at any rate inclusive and perhaps sufficiently audacious to assure the inventor of the title of Dr. Pangloss of controversial memory. But as hard words break no bones I have taken this risk and it would appear to be a convenient “conceptual counter” and even Professor Karl Pearson could not consistently forbid it. It has at any rate the merit of having a meaning clear to all friends and opponents alike of Lamarckism. It will be observed that the two words are placed in what I take to be their natural order as expressive of the Alpha and Omega of the story of organic evolution. The moulding process is claimed to precede that of the sieve, as physiology precedes anatomy and function structure,