The ontogenetic facts which are systematically represented on Plate XII.

and which were first discovered in 1867, deserve the greatest attention, and, indeed, cannot be too highly estimated. They fill up the gap which, according to the opinion of older zoologists existed between the vertebrate and the so-called "invertebrate" animals. This gap was universally regarded as so important and so undeniable, that even eminent zoologists, who were not disinclined to adopt the theory of descent, saw in this gap one of the chief obstacles against it. Now that the ontogeny of the amphioxus and the ascidia has set this obstacle completely aside, we are for the first time enabled to trace the pedigree of man beyond the amphioxus into the many-branching tribe of "invertebrate" worms, from which all the other higher animal tribes have originated.

If our speculative philosophers, instead of occupying themselves with castles in the air, were to give their thoughts for some years to the facts represented on Plates XII. and XIII., as well as to those on Plates II. and III., they would gain a foundation for true philosophy-for the knowledge of the universe firmly based on experience-which would be sure to influence all regions of thought.

These facts of ontogenesis are the indestructible foundations upon which the monistic philosophy of future times will erect its imperishable system.

PLATE XIV. (_Between pages 206 and 207, Vol. II._)

_Monophyletic, or One-rooted Pedigree of the Vertebrate Animal tribe_, representing the hypothesis of the common derivation of all vertebrate animals, and the historical development of their different cla.s.ses during the palaeontological periods of the earth's history. (Compare Chapter XX. vol. ii. p. 192.) The horizontal lines indicate the periods (mentioned in vol. ii. p. 14) of the organic history of the earth during which the deposition of the strata containing fossils took place. The vertical lines separate the cla.s.ses and sub-cla.s.ses of vertebrata from one another. The tree-shaped and branching lines, by their greater or lesser number and thickness, indicate the approximate degree of development, variety, and perfection, which each cla.s.s probably attained in each geological period. In those cla.s.ses which, on account of the soft nature of their bodies, could not leave any fossil remains (which is especially the case with Prochordata, Acrania, Monorrhina, and Dipneusta) the course of development is hypothetically suggested on the ground of arguments derived from the three records of creation-comparative anatomy, ontogeny, and palaeontology. The most important starting-points for the hypothetical completion of the palaeontological gaps are here, as in all cases, furnished by the _fundamental law of biogeny_, which a.s.serts the inner _causal-nexus existing between ontogeny and phylogeny_. (Compare vol. i. p. 310, and vol. ii. p. 200; also Plates VIII.-XIII.) In all cases we have to regard the individual development (determined by the laws of Inheritance but modified by the laws of Adaptation) as short and quick repet.i.tions of the palaeontological development of the tribe. This proposition is the "ceterum censeo" of our theory of development.

The statements of the first appearance, or the period of the origin of the individual cla.s.ses and sub-cla.s.ses of vertebrate animals (apart from the hypothetical filling in mentioned just now), are taken as strictly as possible from palaeontological facts. It must, however, be observed, that in reality the origin of most of the groups probably took place one or two periods earlier than fossils now indicate. In this I agree with Huxley's views; but on Plates V. and XIV. I have disregarded this consideration in order not to go too far from palaeontological facts.

The numbers signify as follows (compare also Chapter XX. and vol. ii.

pp. 204, 206):-1. Animal Monera; 2. Animal Ambae; 3. Community of Ambae (Synambae); 4. Ciliated Infusoria without mouths; 5. Ciliated Infusoria with mouths; 6. Gliding worms (Turbellaria); 7. Sea-sacks (Tunicata); 8. Lancelet (Amphioxus); 9. Hag (Myxinoida); 10. Lamprey (Petromyzontia); 11. Unknown forms of transition from single-nostriled animals to primaeval fishes; 12. Silurian primaeval fish (Onchus, etc.); 13. Living primaeval fishes (sharks, rays, Chimaerae); 14. Most ancient (Silurian) enamelled fishes (Pteraspis); 15. Turtle fishes (Pamphracti); 16. Sturgeons (Sturiones); 17. Angular-scaled enamelled fishes (Rhombiferi); 18. Bony pike (Lepidosteus); 19. Finny pike (Polypterus); 20. Hollow-boned fishes (Closcolopes); 21. Solid boned fishes (Pycnoscolopes); 22. Bald pike (Amia); 23. Primaeval boned fishes (Thrissopida); 24. Bony fishes with air pa.s.sage to the swimming bladder (Physostomi); 25. Bony fishes without air pa.s.sage to the swimming bladder (Physoclisti); 26. Unknown forms of transition between primaeval fishes and amphibious fishes; 27. Ceratodus; 27_a_. Extinct Ceratodus from the Trias; 27_b_. Living Australian Ceratodus; 28. African amphibious fishes (Protopterus) and American amphibious fishes (Lepidosiren); 29. Unknown forms of transition between primaeval fishes and amphibia; 30. Enamelled heads (Ganocephala); 31. Labyrinth toothed (Labyrinthodonta); 32. Blind burrowers (Caeciliae); 33. Gilled amphibia (Sozobranchia); 34. Tailed amphibia (Sozura); 35. Frog amphibia (Anura); 36. Dichthacantha (Proterosaurus); 37. Unknown forms of transition between Amphibia and Protamnia; 38. Protamnia (common primary form of all Amnion animals); 39. Primary mammals (Promammalia); 40. Primaeval reptiles (Proreptilia); 41. (Thecodontia); 42. Primaeval dragons (Simosauria); 43. Serpent dragons (Plesiosauria); 44. Fish dragons (Ichthyosauria); 45. Teleosauria (Amphicla); 46. Steneosauria (Opisthocla); 47. Alligators and Crocodiles (Prosthocla); 48.

Carnivorous Dinosauria (Harpagosauria); 49. Herbivorous Dinosauria (Therosauria); 50. Maestricht lizards (Mosasauria); 51. Common primary form of Serpents (Ophidia); 52. Dog-toothed beaked lizards (Cynodontia); 53. Toothless beaked lizards (Cryptodontia); 54. Long-tailed flying lizards (Rhamphorhynchi); 55. Short-tailed flying lizards (Pterodactyli); 56. Land tortoises (Chersita); 57. Birds-reptiles (Tocornithes), transition form between reptiles and birds; 58. Primaeval griffin (Archaeopteryx); 59. Water beaked-animal (Ornithorhynchus); 60.

Land beaked-animal (Echidna); 61. Unknown forms of transition between Cloacals and Marsupials; 62. Unknown forms of transition between Marsupials and Placentals; 63. Tuft Placentals (Villiplacentalia); 64.

Girdle Placentals (Zonoplacentalia); 65. Disc Placentals (Discoplacentalia); 66. Man (h.o.m.o pithecogenes, by Linnaeus erroneously called, h.o.m.o sapiens.)

PLATE XV. (_After page 369, Vol. II._)

_Hypothetical Sketch of the Monophyletic Origin and the Diffusion of the Twelve Species of Men from Lemuria over the earth._ The _hypothesis_ here geographically sketched of course only claims an entirely _provisional value_, as in the present imperfect state of our anthropological knowledge it is simply intended to show how the distribution of the human species, from a single primaeval home, may be _approximately_ indicated. The probable primaeval home, or "Paradise," is here a.s.sumed to be _Lemuria_, a tropical continent at present lying below the level of the Indian Ocean, the former existence of which in the tertiary period seems very probable from numerous facts in animal and vegetable geography. (Compare vol. i. p. 361, and vol. ii. p. 315.) But it is also very possible that the hypothetical "cradle of the human race" lay further to the east (in Hindostan or Further India), or further to the west (in eastern Africa). Future investigations, especially in comparative anthropology and palaeontology, will, it is to be hoped, enable us to determine the probable position of the primaeval home of man more definitely than it is possible to do at present.

If in opposition to our monophyletic hypothesis, the polyphyletic hypothesis-which maintains the origin of the different human species from several different species of anthropoid ape-be preferred and adopted, then, from among the many possible hypotheses which arise, the one deserving most confidence seems to be that which a.s.sumes a double pithecoid root for the human race namely, an Asiatic and an African root. For it is a very remarkable fact, that the African man-like apes (gorilla and chimpanzee) are characterized by a distinctly long-headed, or dolichocephalous, form of skull, like the human species peculiar to Africa (Hottentots, Caffres, Negroes, Nubians). On the other hand, the Asiatic man-like apes (especially the small and large orang), by their distinct, short-headed, or brachycephalous, form of skull agree with human species especially characteristic of Asia (Mongols and Malays).

Hence, one might be tempted to derive the latter (the Asiatic man-like apes and primaeval men) from a common form of brachycephalous ape, and the former (the African man-like apes and primaeval men) from a common dolichocephalous form of ape.

In any case, tropical Africa and southern Asia (and between them Lemuria, which formerly connected them) are those portions of the earth which deserve the first consideration in the discussion as to the primaeval home of the human race; America and Australia are, on the other hand, entirely excluded from it. Even Europe (which is in fact but a western peninsula of Asia) is scarcely of any importance in regard to the "Paradise question."

It is self-evident that the migrations of the different human species from their primaeval home, and their geographical distribution, could on our Plate XV. be indicated only in a very general way, and in the roughest lines. The numerous migrations of the many branches and tribes in all directions, as well as the very important re-migrations, had to be entirely disregarded. In order to make these latter in some degree clear, our knowledge would, in the first place, need to be much more complete, and secondly, we should have to make use of an atlas with a number of plates showing the various migrations. Our Plate XV. claims no more than to indicate, in a very general way, the approximate geographical dispersion of the twelve human species as it existed in the fifteenth century (before the general diffusion of the Indo-Germanic race), and as it can be sketched out approximately, so as to harmonize with our hypothesis of descent. The geographical barriers to diffusion (mountains, deserts, rivers, straits, etc.), have not been taken into consideration in this general sketch of migration, because, in earlier periods of the earth's history, they were quite different in size and form from what they are to-day. The gradual trans.m.u.tation of catarrhine apes into pithecoid men probably took place in the tertiary period in the hypothetical Lemuria, and the boundaries and forms of the present continents and oceans must then have been completely different from what they are now. Moreover, the mighty influence of the ice period is of great importance in the question of the migration and diffusion of the human species, although it as yet cannot be more accurately defined in detail. I here, therefore, as in my other hypotheses of development, expressly guard myself against any dogmatic interpretation; they are nothing but _first attempts_.