d) Classification. The so-called Tree of Life. All living forms can be arranged in a diagram called the Tree of Life. The Tree has a short trunk, indicating common origin of the living from the non-living, and is divided into two large trunks representing plants and animals respectively. "From each of these start large branches representing classes, the larger branches giving off smaller branches representing families, and so on with smaller and smaller branches representing orders and genera, until we come to leaves as representing species, the height of the branch from which they are hanging indicating their place in the growth of the great life-tree." (Clodd, _"Story of Creation,"_ p. 103.) There is an exact gradation from the lowest life forms to the highest. First such simple forms as the sponges and corals, then, through the worms, crabs, oysters, and snail to the fish, and thence through amphibia, reptiles, beasts of prey, ungulates (hoofed animals) and apes to man. Evolutionists say that in this gradation of life we see illustrated the evolution of complex from simple forms. The Descent of Man. According to the evolutionary hypothesis man is related to the animal kingdom by descent from a brute ancestor, who, apelike in appearance, is the common ancestor of ape and man. The evidence of such derivation is believed to be: i. Rudiments of structure which were useful in some brute ancestor. There remain in man a few elementary muscles for twitching the skin, as in the forehead; and it is pointed out that many animals have such muscles at the present time, and it is argued that the ability of some men to move the whole scalp points to the existence of muscles with such function in our brute ancestors. The vermiform appendix in man is termed rudimentary, being but a remnant of the much longer and more complex appendix of the same nature in living animals today. 2. Embryonic Development. Because the young of all animals resemble one another while in the embryo stage, and since such resemblances are found in man, it is concluded that the evolution of man from some related animal form must be accepted as the most reasonable explanation. 3. Some diseases are common to animals and man (tuberculosis, cholera, hydrophobia, etc.). 4. The similarity in structure of man and the apes. 5. The fossil remains of man. Certain skulls and leg bones have been found which are said to represent forms higher than the ape and lower than man. On the strength of such finds it is said that the "missing link" has now been supplied. The Nebular Hypothesis.