Analogous preadaptations occur in conjunction with the phenomena of parasitism, symbiosis and commensalism, all of which offer instances of otherwise disparate and unrelated organisms that are inseparably bound together, in some apparently capricious and fortuitous respect, by a preadaptation of the one to the other. Parasites, guests, or symbiotes, as the case may be, they are now indissolubly wedded to some determinate species of host by reason of an appropriate and congenital adjustment. For all that, however, the association seems to be a contingent one, and it appears incredible that the associates were always united, as at present, by bonds of reciprocal advantage, mutual dependence, or one-sided exploitation. Yet the basis of the relationship is in each case a now inherited adaptation, which, if it does not represent the primitive condition of the race, must at some time have been acquired. For phenomena such as these, orthogenesis, which makes an organ the exclusive product of internal factors, conceiving it as a preformed mechanism that subsequently selects a suitable function, has no satisfactory explanation. Lamarckism, which asserts the priority of function and makes the environment mold the organ, is equally inacceptable, in that it flouts experience and ignores the now demonstrated existence of internal hereditary factors. But, if between these two extremes some evolutionary _via media_ could be found, one must confess that it would offer the only conceivable “natural explanation” of preadaptation.[6] All this, of course, is pure speculation, but it serves to show that here, at any rate, the theory of Transformism occupies a position from which it cannot easily be dislodged. [6] Vernon Kellogg has expressed this same view in a recent article, though he frankly admits that it is an as yet unrealized desideratum. “Altogether,” he says, “it must be fairly confessed that evolutionists would welcome the discovery of the actual possibility and the mechanism of transferring into the heredity of organisms such adaptive changes as can be acquired by individuals in their lifetime. It would give them an explanation of evolution, especially of adaptation, much more satisfactory than any other explanation at present claiming the acceptance of biologists.” (_Atlantic Monthly_, April, 1924, p. 488.)