seven great divisions. Each of these is further divided into several principal classes, and each principal class into lesser classes. For instance, the mammals form one class of the vertebrata. Hæckel divides the class of mammals into three inferior classes, each inferior class into legions, the legions into orders, the orders into inferior orders or sections, the sections into families, the

families into genera. Each genus comprises, according

to the ordinary view, as we have already seen, several species, and a species again may comprise several varieties. Now this natural system, with its divisions and subdivisions, can very well be drawn out in the form of a genealogical tree; first of all comes the general term animal, then follow the principal divisions, the vertebrate animals, molluscs, etc., under the vertebrate animals come the principal classes, and so on down to the varieties. This representation shows the greater or lesser resemblance of the separate groups, or figuratively speaking, their relationship. So far all is undisputed. But then Hæckel comes in and says, the expression "related" has not only a figurative, but a literal meaning; the ideal relationship rests on genetical relationship, the species related in form are related in blood, the pedigree of the so-called natural system, in which men of science have placed the different forms according to their greater or lesser degree of resemblance, is the real pedigree of organisms. All the different forms of the domestic cat are descendants of one primæval ancestor who represented the species Felis domestica. The genus Felis comprises besides

on a

1 Natürliche Schöpfungsgeschichte, pp. 364, 400. Über die Entstehung, etc. p. 15. Anthropogenie, p. 88.

the domestic cat, the lion, the tiger, etc. All these different species of the genus Felis resemble one another so much in the shape of their bodies, in the form of the jaw and of the foot, that we may suppose that they have all sprung from one single ancestral cat. In the same way we consider that the genera cats and hyænas which we combine in the family of catlike wild beasts, Felina, are descendants of one single cat-like beast of prey, which lived at a much earlier period of the world's history than the ancestral cat. In the same way all the dog-like wild beasts, Canina, are descended from one primæval dog-like ancestral form; the Ursina from a bear-like form, and so on.

Now we find that all these cat-like, dog-like, bear-like, and other animals resemble one another in some important zoological parts, principally in the form of the jaw and the foot; and, on the other hand, they differ quite plainly from all other kinds of mammals. For this reason all these families are included in one larger group, the order of the beasts of prey, or flesh-eaters, carnivora. According to Darwin's theory, these beasts of prey are all descended from one common ancestral form, and naturally this primæval beast of prey, the ancestor of the whole order of beasts of prey, must have existed much earlier than did the ancestors of the separate families of beasts of prey.

The other orders of mammals, the rodents, the apes, the marsupials, must have had a common ancestor, like the beasts of prey. All these orders of the class of mammals resemble one another in the fact which gives them their name, that the young are fed by the mother's milk; and also in several important portions of

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G

their internal structure. These common characteristics separate the mammiferous animals from the other classes of vertebrate animals, the birds, reptiles, amphibious animals, and fish. Thus all the mammiferous animals, however different they may be, resemble one another more nearly, i.e. they are more closely related, than any mammal resembles a bird or a reptile. In the same way all birds on the one hand, all reptiles on the other, resemble each other much more than any bird resembles a reptile. In all zoological systems these differences and resemblances are expressed in this way-all the orders of mammals are included in the class of mammals, all orders of birds in the class birds, all orders of reptiles in the class reptiles. According to Darwin, this systematic arrangement is founded on the fact that all the mammals have sprung from a common primitive mammalian ancestor, all birds from an ancient ancestral bird, all reptiles from a common reptile form.

If we go a step further, we see that all mammals, birds, reptiles, amphibious animals, and fish may be brought under the common head of vertebrate animals. The vertebrata resemble one another in several important particulars, for instance in the peculiar formation of the skeleton and the nervous system, while they differ in the same ways from the mollusca, articulata, etc. Consequently we must also assume a common form for all vertebrata, and also for all mollusca, etc.; so that at some period—no doubt a very long time ago—there were only seven different forms of animals, a vertebrate, a mollusc, etc. These seven are all descended from a moneron which came into existence by spontaneous generation.1

1 See above, pp. 9 and 10.

only does the natural

According to this view, not system of animals and plants arrange the different forms in parallel or consecutive groups, according to their greater or lesser degree of resemblance, and by this means facilitate the survey of the enormous number of forms; nor is the natural system of organisms only intended to give us a short summary of our anatomical knowledge concerning the forms of the various groups; it also reveals to us the blood relationship of the organisms, and displays their real and actual pedigree." Or in other words, "the natural system of organisms is only the expression of the phylogeny of organisms; of the gradual branching out from the first simple ancestral form into the multiplicity of individual forms.”

So says Hæckel.' It sounds very simple. But is this analogy between the genealogical arrangement of the system and the pedigree given in the Darwinian theory really a proof of the latter? Not in the least. The explanation I have just quoted is really intended to show us that if all animals are in reality descended from one single form, or from a few primitive forms, we must suppose that the genealogy of the animal world is something of this kind. Surely we must not assume this to be really the case, for this is just what has got to be proved. If the pedigree is to take rank as a real genealogical pedigree, it must be possible to prove in detail that the individuals which are put down in it as allied by blood are really descended from common ancestors, or may possibly be so descended; and to show not only that the cat, the lion, the tiger, 1 Ueber die Entstehung, p. 20.

etc., may possibly be descended from a primitive cat, but also that this primitive cat, the primitive dog and bear, etc., are descended from the same primitive carnivorous animal, and the primitive mammal, bird, and fish, etc., from one primitive vertebrate animal. I have shown in the preceding lectures what great objections there are to this supposition, and how little the facts bear it out.

Further, if a pedigree is to be considered genuine, it must at any rate be proved that those individuals which are set down as members of it and as ancestors of other members, have really existed. Hæckel himself says, "For if the theory of descent is really true, if the petrified remains of formerly living animals and plants really proceed from the extinct primæval ancestors and progenitors of the present organisms, then without anything else the knowledge and comparison of fossils ought to disclose to us the pedigree of organisms."1

But he at once admits that this is still only very imperfectly the case, and that "we are still dependent upon very many uncertain hypotheses, when actually endeavouring to sketch the pedigree of the different organic groups. We must not allow Hæckel's very detailed and elaborate pedigree to impose upon us; no doubt no single member is absent; everything is given just as accurately and completely as the pedigree of the royal house of Germany in a historical work. But if we look more closely at the way in which Hæckel has obtained all the names, we soon see