With marvellous vigour and quickness of perception he applied the principles of Evolution or the theory of descent to the whole organic world, and not only opened entirely new vistas for the study of morphology, but also worked them out and fixed them. He was the first to draw up pedigrees of the various larger groups of animals and plants, filling the gaps by fossils or with hypothetical forms (the necessary existence of which he arrived at by logical deductions); and thus he reconstructed the first universal pedigree, a gigantic ancestral tree, from the simple unicellular Amoeba to Man. Of course these pedigrees were entirely provisional, as he himself has over and over again avowed; but they are, nevertheless, the ideal which all systematists and morphologists working upon the basis of Evolution have since been seeking to establish. Naturally he was vigorously attacked, not only by anti-Darwinians, or rather anti-Evolutionists, but also by many of those who, having accepted the principle of transformism, ought to have known better. Perhaps they thought they did know better. Imperfections or mistakes in details of the grand attempt,--and these, naturally, were many,--were singled out as samples of the whole, which was ridiculed as the romance of a dreamer. In the end, however, this hostility, narrow-minded and unfair in many respects, has done good to the cause. There has arisen an ever-increasing school of workers in favour of the new doctrine. Owing to renewed research, criticism, corrections in all directions, we now know considerably more about natural classification (and this is pedigree) than when Haeckel first opened out the whole problem. Owing to his fearless mode of exposition, regardless of the indignant wrath which the new doctrine aroused in certain ecclesiastical quarters, Haeckel bore the brunt of almost endless attacks, and had to write polemical essays. The result has been that friend and foe alike are now working on the lines which he has laid down; most of the ideas which he was the first to conceive, and to formulate by inventing a scientific terminology for them, have become important branches, or even disciplines, of the science. Most morphologists of the younger generations now take these terms for granted, without remembering the name of their founder. It is, therefore, perhaps not quite superfluous to mention some of them: _Phylum_, or stem, the sum total of all those organisms which have probably descended from one common lower form. He distinguished eight such phyla--Protozoa, Coelenterata, Helminthes or Vermes, Tunicata, Mollusca, Articulata, and Vertebrata. The phyla are more or less analogous to 'super-classes,' large branches or 'circles,' or principal groups of other zoologists. _Phylogeny_, the history of the development of these various phyla, classes, orders, families, and species.