on this plan and are characteristic structures of the Paleozoic age. The fishes are the first animals with backbones. The earlier types were covered with heavy coats of mail like the gar pike of our inland lakes. The shark represents, perhaps, the basic form, a great mass without sharp division of head, body and tail. The next stage is represented by amphibious creatures which have gills during their early life. Typical of this form are the salamanders and frogs. These yield place to the reptiles, the lizard bearing close resemblance to the early types. Snakes are but degenerate lizards. From the reptiles it is but a short step to the birds, the scales being modified feathers, the forelegs to wings. The apteryx of Australia is a transitional form, while penguins and ostriches are wingless so far as flight is concerned. The Mesozoic age in which such types are dominant is thus one of transition. Lowest among the mammals are the duckbill and its relative the echidna which superficially resembles the hedgehog. Both lay eggs. The next stage is represented by the marsupials, the so-called Tasmanian wolf, the kangaroo, the opossum of America. Here the young are born in extremely immature condition and must be carried in a pouch on the body of the mother. This brings us to the true placenta-bearing mammals divided into many orders. The great development of mammals took place during the Cenozoic or Tertiary age, though clear records of man are not found until the recent or Quaternary. Such is the scale from the lowest to the highest of living forms and this corresponds with the order of their appearance in the rocks. Evolution Accepted Such facts as those above indicated have forced thinking men to believe in a process of evolution. Against this interpretation there are no physical facts and its opponents are forced to arguments on theoretical or theological grounds. As a matter of fact, there would be little opposition to the theory if it were not for the inclusion of man as a product of organic development. But no physical reason for excluding him can be found. Evolution, then, is but a name for the processes of organic history. It carries no other meaning or implication. It must explain degeneration and retrogression as well. It has no moral connotation. It does not say that things are getting better or worse. It is but an attempt to understand and it represents the best thought of the best trained minds. As such it is likely to stand until further information makes revision necessary. Darwin studied for twenty years without publishing his ideas. Most of the opponents of evolution appear to publish for twenty years without preliminary study. A tremendous amount of work remains to be done ere we shall have a satisfactory picture of the history of life on earth. Great areas like northern Asia where many of the early events seem to have taken place are almost unexplored. But the age of field work draws to a close and the interest of students has shifted. To-day they are studying heredity rather than evolution, and we must follow their trail. REFERENCES 1. Quoted by W. RILEY, From Myth to Reason, p. 166. 2. Quoted by R. S. LULL, Ways of Life, p. 311. 3. Quoted by A. D. WHITE, Warfare of Science and Theology, р. 46. 4. Ibid., p. 55. 5. Quoted by H. F. OSBORN, From the Greeks to Darwin, p. 129. 6. Ibid., p. 132. 7. Ibid., p. 133. 8. Quoted by E. CLODD, Pioneers of Evolution, p. 112. 9. Ibid., p. 113. 10. V. L. KELLOGG, Darwinism Today, pp. 2-3. 11. J. А. ТнOMSON, Darwinism and Human Life, p. 199. 12. Ibid., p. 200. 13. F. S. CHAPIN, Social Evolution, p. 26. 14. E. C. MOORE, Old Penn, Dec. 14, 1914, p. 361. CHAPTER XI HEREDITY My gifts have come to me from down the years: Some gave me purity, some gave the grime -BARKER CELLS AND THEIR FUNCTIONS While our understanding of the process of reproduction is far from complete we have found out more since 1850 than man had discovered in all the earlier time. Long ago man had learned that plants came from seeds; that animals reproduced "each after its kind"-lions begetting lions, and elephants, elephants. The Romans saw that some traits descended in family lines and spoke of certain families as capitones and labiones, just as modern Europeans have spoken The following is a key to the diagrams in this chapter: -Males -Females -Sex unknown -Stillborn or died in early infancy. Shaded symbols represent individuals showing the character under discussion. of the Hapsburg lip. The Israelites are said to have tried some breeding experiments with their cattle. Tacitus explained the uniform features of the Germans by claiming that they were of common and unmixed descent. Nevertheless, no great amount of information was secured until the microscope widened the range of human vision. So marvelous have been its revelations, especially since 1880 when aniline dyes came into use, that the center of biological interest has shifted from the adult to the cell. As early as 1651 William Harvey asserted that all living organisms came from eggs. In 1665 Robert Hooke, examining a section of cork under the microscope, saw that it was made of "little boxes or cells distinguished from one another." By 1677 the human spermatozoön was discovered. In 1759 Wolff caught the idea that growth resulted from the multiplication of these small cells. In 1831 Robert Brown found that the plant cell had a nucleus. In 1835 Felix Dujardin discovered protoplasm, which is called "the material basis of life" and which always exists in cellular form. In 1838 Schleiden and Schwann demonstrated that plant and animal cells were similar in structure. In 1861 Gegenbauer showed that the eggs of all vertebrates were, in reality, single cells. This was found to be true of the spermatozoa in 1865. Multiplication and Growth crease. From these discoveries man learned that all forms of life start as single cells and that growth is the result of their inBut many forms do not enlarge-they simply divide and separate, and there are two cells where there was one before. When the cells divide (the process is called mitosis), in the multicellular forms, they do not separate but remain in close association in what we call a body. There comes also an increasing specialization in cell functions whose cause is unknown. A begonia leaf put in a saucer of water may start to grow and, if conditions are favorable, may develop |