Against this view there is an argument which has hitherto only been glanced at, but which must now be discussed in more detail. It is represented in a recent work by Prof. Conrad Günther, one of the latest champions of the theory of chance variations and natural selection as the sole explanation of evolution, who has assembled a number of instances to show that the “purposive force” which biologists are now coming to believe in “often fails in living beings.” Such are, for example, the fact that an _Amœba_ seeking nourishment will take in a particle of stone or anything that comes in its way;[111] that the mutual relations of flowers and insects are often unsuitable; that a bee will sting a human being just as it will another insect, although the sting, only meant for the latter kind of use, cannot be withdrawn from the human skin; that embryos often go astray during development; that a cricket which tries to escape in the open by burying itself in the earth will act similarly if you set it on a glass plate; and so forth. Nature, of course, teems with such cases—one might add the singular degeneration of the slave-making ants already described in some detail.[112] “If,” he concludes, “the purposive reaction in the vital force of animals were independent of the external world, they would be armed against all contingencies, and that is not the case.”[113] Thus, too, Prof. Eimer, who in dealing with cases where the alleged X factor in Nature has gone wrong, writes:— “The zoologist can hardly accept the existence of such a dominant inner factor ever pushing toward advance, when he recalls the host of regressive structures which he has to see.”[114] Now when the cause of physico-chemical _versus_ vital agencies comes to be tried, not in the laboratory but in the study, not by science but by philosophy, the first question that will be asked is, What, then, is your distinction between ‘vital’ and ‘physico-chemical’ energies? How are we to recognize when we are in presence of the one or of the other? The usual answer to this searching question is that in vital agency we find a directive, a purposeful, a psychic element, whereas physico-chemical energies seem to be nothing but the play of a blind, indifferent mechanism. But, it will be rejoined, how can any one affirm that physico-chemical energies are not also vital, directive, psychic? Is there not, in fact, something psychic in the very conception of energy? To these questions there seems to me no conceivable reply. When a ‘vital’ energy has been reduced to a ‘physico-chemical,’ we have evidently explained nothing—we have only exchanged one mystery for another.