Personal conviction [he writes],[213] mere possibility, are offered as proofs, or at least as arguments in favour of the theory. Can we admit their validity? Obviously not. The human mind can conceive many things: is that a reason for accepting them all?... Obviously more serious proofs are needed. After all, save where a contradiction is involved, everything is _possible_.... If adopting, under the shadow of Oken's great name, his principle of the repetition of phenomena, a naturalist should maintain that each of the planets has its own Europe, its England, and its Darwin expounding to the Jovians and Saturnians the origin of species, I do not quite see how one would set about showing him that he was wrong. Unquestionably the thing is _possible_. Are we to draw the conclusion that it is a fact? Again,[214] the same distinguished naturalist, having quoted Darwin's very elaborate explanation of a difficulty, remarks: We see how with Darwin, as with his precursors, one hypothesis necessitates another. But can he, at least, by means of these subsidiary theories, these comparisons, these metaphors, account for all the facts? No, he himself honestly confesses more than once that he cannot. It is true that he adds "I am convinced that the objections have little weight, and the difficulties are not insoluble." But is this conviction of his a proof, or even an argument? M. Blanchard likewise comments vigorously on this mode of argumentation. Speaking of the Mole and Darwin's explanation of its blindness, namely that having taken to living under-ground it lost its eyes through disuse--which he considers a most preposterous supposition,--M Blanchard continues:[215] The realms of fancy are boundless; but the observer who is concerned with realities can only have recourse to the facts of science. Fossil remains discovered in very ancient strata show that the underground animal of present times does not differ from his geological counterpart. The Mole belongs to a very peculiar type, and has no nearer European relatives than the Hedgehog and the Shrew. Can we imagine a common ancestor of Shrews, Hedgehogs, and Moles? On this point Mr. Darwin expresses no opinion,--which should not be, for when confronted by forms clearly differentiated, he is wont to extricate himself from difficulties with matchless facility. The intermediate links, he will say, were doubtless less fitted to live than were the others, and so have disappeared. After _that_ the Evolutionists consider any one quite out of date who does not consider himself entirely satisfied with so felicitous an explanation. M. de Quatrefages denounces another fatal defect often observable in the method of proof.