The great problems still remaining for solution, which have hardly been touched by modern biology in all its endeavours to find a mechanical explanation of the living machine, are, therefore, three. First, the relation of mentality to the general phenomena of the correlation of force; second, the intelligible understanding of the mechanism of protoplasm which enables it to guide the blind chemical and physical forces of nature so as to produce definite results; third, the kind of forces which may have contributed to the origin of that simplest living machine upon whose activities all vital phenomena rest--the living cell. INDEX. A. Absorption of food, 20. Acquired characters, inheritance of, 164, 165, 166, 167, 171. --variations, 159, 160. Amoeba, 73. Anatomical evidence for evolution, 142. Aquacity, 80. Arm compared with wing, 144. Aristotle, 1. Assimilation, 80, 124, 149, 176. Asters of dividing cells, 98. B. Barry, 63, 64. Bathybias, 84. Biology a new science, 1, 5, 15. Blood, 35, 36, 38, 69, 73. Blood-vessels, 35, 36. Body as a machine, 22, 25, 49. Bone cells, 69. Building of the living machine, 131, 134, 136, 137, 167, 175, 180. C. Cartilage cells, 68. Cell as a machine, 126, 128. --description of, 69. --division, 95, 96, 101. --discovery of, 58. --doctrine, 60. --substance, 65, 125. Cells, 56, 84, 86, 118, 119. Cellular structure of organisms, 65. Cell wall, 64, 72. Centrosome, 94, 96, 97, 101, 103, 105, 110. Challenger expedition, 83. Chemical evolution, 179. Chemical theory of vitality, 14; of life, 78, 116. Chemism or mechanism, 57, 176. Chemistry of digestion, 27, 28; of protoplasm, 76; of respiration, 38. Chromatin, 92, 94, 96, 102, 149, 153. Chromosomes, 97, 98, 101, 105, 108, 110, 113, 152. Circulation, 34. Colonies of cells, 85. Comparison of the body and a machine, 22. Congenital variations, 158, 160, 163; inheritance of, 164. Connective-tissue cells, 70. Conservation of energy, 7, 17. Consciousness as a factor in machine building, 173. Constructive chemical processes, 50, 51, 52, 124. Continuity of germ plasm, 155. Correlation of vital and physical forces, 13, 16, 22, 23, 24, 25. Cytoblastema. 62. Cytology, 10. D. Darwin, 81. Death of the cell, 127. Decline of the reign of protoplasm, 85. Destructive chemical processes, 50, 51, 52, 125. Dialysis, 29, 30, 31. Digestion, 27. E. Egg, 103, 120, 152. division of, 63. Egg, fertilization of, 102. Embryological evidence for evolution, 140. Energy of nervous impulse, 43, 54. Environment, 171. Evidence for evolution as a method of machine building, 139, 145. Evolution, 9, 16, 81, 134. Experiments with developing eggs, 121. F. Fat, absorption of, 32. Female pronucleus, 110. Fern cells, section of, 67. Fertilization of the egg, 95, 102; significance of, 112. Fibres in protoplasm, 87; --in spindle, 98, 101. Forces at work in machine building, 148, 176, 181. Formed material, 64.