It is a great work. How few there are in the whole of the nineteenth century that show the wealth of ideas we find in the first volume alone.[4] And this is only one volume. We have as yet said nothing of the idea that is of the greatest consequence in connection with Haeckel’s own development. He was a Darwinian from 1862 onwards. After 1866 and the publication of the _General Morphology_ we find him dominated in all his work by one single idea from the Darwinian group. He brought this idea so effectively to the front, improved and developed it so assiduously, and applied it in so many ways, that it has come to be regarded as his own most characteristic work. It is inseparable from his name. Whatever the future may be, wherever Haeckel’s name is uttered people will add the phrase that was made peculiarly his after 1866, that colours and pervades all his works—technical, popular, polemical, or philosophical—as much as the word “Monism.” It is the phrase: the biogenetic law. Footnote 4: The reader may be interested to know that Haeckel gives a popular summary of his early work on individuality and on the mathematical types of organisms in a more recent work. This has been translated into English with the title _The Wonders of Life_. The two chapters that deal with these questions are omitted from the abridged cheap edition. [Trans.] Here and there even in the first volume of the _Morphology_ a note is struck that the reader cannot clearly understand. It increases in the second volume until it dominates the whole book. The phrase is known far and wide to-day. This is partly due to Haeckel’s own insistence on it, but perhaps still more to the real value of the idea itself. It crops up in a hundred different fields—psychology, ethics, philosophy, even in art and æsthetics. I have been able to trace it even into modern mysticism. For the moment I will only point out that it has been attacked and misstated with real fanaticism, in spite of the splendid and perfectly clear account of it that Haeckel has given.