When Professor Ray Lankester goes on to speak of the “undemonstrable agencies” “arbitrarily asserted” to exist by Professor Semper, he is again presuming on the ignorance of his readers. Professor Semper’s agencies are in no way more undemonstrable than Mr. Darwin’s are. Mr. Darwin was perfectly cogent as long as he stuck to Lamarck’s demonstration; his arguments were sound as long as they were Lamarck’s, or developments of, and riders upon, Buffon, Erasmus Darwin, and Lamarck, and almost incredibly silly when they were his own. Fortunately the greater part of the “Origin of Species” is devoted to proving the theory of descent with modification, by arguments against which no exception would have been taken by Mr. Darwin’s three great precursors, except in so far as the variations whose accumulation results in specific difference are supposed to be fortuitous—and, to do Mr. Darwin justice, the fortuitousness, though always within hail, is kept as far as possible in the background. “Mr. Darwin’s arguments,” says Professor Ray Lankester, “rest on the _proved_ existence of minute, many-sided, irrelative variations _not_ produced by directly transforming agents.” Mr. Darwin throughout the body of the “Origin of Species” is not supposed to know what his variations are or are not produced by; if they come, they come, and if they do not come, they do not come. True, we have seen that in the last paragraph of the book all this was changed, and the variations were ascribed to the conditions of existence, and to use and disuse, but a concluding paragraph cannot be allowed to override a whole book throughout which the variations have been kept to hand as accidental. Mr. Romanes is perfectly correct when he says {232a} that “natural selection” (meaning the Charles-Darwinian natural selection) “trusts to the chapter of accidents in the matter of variation” this is all that Mr. Darwin can tell us; whether they come from directly transforming agents or no he neither knows nor says. Those who accept Lamarck will know that the agencies are not, as a rule, directly transforming, but the followers of Mr. Darwin cannot.