Romantic nature of embryology, 195. Its importance, 195. Rudimentary organs and their meaning, 195. The domain of embryology, 196. Five historical periods, 196. The period of Harvey and Malpighi, 197-205. The embryological work of these two men insufficiently recognized, 197. Harvey's pioneer attempt critically to analyze the process of development, 198. His teaching regarding the nature of development, 199. His treatise on Generation, 199. The frontispiece of the edition of 1651, 201, 202. Malpighi's papers on the formation of the chick within the egg, 202. Quality of his pictures, 202. His belief in pre-formation, 207. Malpighi's rank as embryologist, 205. The period of Wolff, 205-214. Rise of the theory of pre-delineation, 206. Sources of the idea that the embryo is pre-formed within the egg, 207. Malpighi's observations quoted, 207. Swammerdam's view, 208. Leeuwenhoek and the discovery of the sperm, 208. Bonnet's views on _emboîtement_, 208. Wolff opposes the doctrine of pre-formation, 210. His famous Theory of Generation (1759), 210. Sketches from this treatise, 209. His views on the directing force in development, 211. His highest grade of work, 211. Opposition of Haller and Bonnet, 211. Restoration of Wolff's views by Meckel, 212. Personal characteristics of Wolff, 213. The period of Von Baer, 214-222. The greatest personality in embryology, 215. His monumental work on the Development of Animals a choice combination of observation and reflection, 215. Von Baer's especial service, 217. Establishes the germ-layer theory, 218. Consequences, 219. His influence on embryology, 220. The period from Von Baer to Balfour, 222-226. The process of development brought into a new light by the cell-theory, 222. Rathke, Remak, Koelliker, Huxley, Kowalevsky, 223, 224. Beginnings of the idea of germinal continuity, 225. Influence of the doctrine of organic evolution, 226. The period of Balfour, with an indication of present tendencies, 226-236. The great influence of Balfour's Comparative Embryology, 226. Personality of Balfour, 228. His tragic fate, 228. Interpretation of the embryological record, 229. The recapitulation theory, 230. Oskar Hertwig, 232. Wilhelm His, 232. Recent tendencies; Experimental embryology, 232; Cell-lineage, 234; Theoretical discussions, 235. CHAPTER XI The Cell-Theory--Schleiden. Schwann. Schultze, 237