49. Bichat, 1771-1801, 169 50. Von Koelliker, 1817-1905, 173 51. Rudolph Virchow, 1821-1903, 174 52. Franz Leydig, 1821-1908 (April), 175 53. S. Ramon y Cajal, 176 54. Albrecht Haller, 1708-1777, 182 55. Charles Bell, 1774-1842, 184 56. Johannes Müller, 1801-1858, 187 57. Ludwig, 1816-1895, 188 58. Du Bois-Reymond, 1818-1896, 189 59. Claude Bernard, 1813-1878, 191 60. Frontispiece of Harvey's _Generatione Animalium_ (1651), 201 61. Selected Sketches from Malpighi's Works, 203 62. Marcello Malpighi, 1628-1694, 204 63. Plate from Wolff's _Theoria Generationis_ (1759), 209 64. Charles Bonnet, 1720-1793, 212 65. Karl Ernst von Baer, 1792-1876, 216 66. Von Baer at about Seventy Years of Age, 217 67. Sketches from Von Baer's Embryological Treatise (1828), 221 68. A. Kowalevsky, 1840-1901, 225 69. Francis M. Balfour, 1851-1882, 227 70. Oskar Hertwig in 1890, 231 71. Wilhelm His, 1831-1904, 233 72. The Earliest Known Picture of Cells, from Hooke's _Micrographia_ (1665), 238 73. Sketch from Malpighi's Treatise on the Anatomy of Plants (1670), 239 74. Theodor Schwann, 1810-1882, 245 75. M. Schleiden, 1804-1881, 246 76. The Egg and Early Stages in Its Development (after Gegenbaur), 253 77. An Early Stage in the Development of the Egg of a Rock Limpet (after Conklin), 254 78. Highly Magnified Tissue-Cells from the Skin of a Salamander (after Wilson), 255 79. Diagram of the Chief Steps in Cell-Division (after Parker), 256 80. Diagram of a Cell (modified after Wilson), 257 81. (_A_) Rotation of Protoplasm in Cells of Nitella. (_B_) Highly Magnified Cells of a Tradescantia Plant, Showing Circulation of Protoplasm (after Sedgwick and Wilson), 261 82. Félix Dujardin, 1801-1860, 265