CONTENTS XV 
Bonnet’s views on embo?tement, 208. Wolff opposes the divcitine 
of preformation, 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 Wollfi’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 proc- 
ess 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. Person- 
ality 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 NI 
THE CELL-THEORY—SCHLEIDEN. SCHWANN. SCHULTZE, 237 
Unifying power of the cell-theory, 237. Vague foreshadowings, 237. 
The first pictures of cells from Robert Hooke’s Micrographia, 238. 
Cells as depicted by Malpighi, Grew, and Leeuwenhoek, 239, 240. 
Wolff on cellular structure, 240, 241. Oken, 241. The an- 
nouncement of the cell-theory in 1838-39, 242. Schleiden and 
Schwann co-founders, 243. Schleiden’s work, 243. His ac- 
quaintance with Schwann, 243. Schwann’s personal appearance, 
244. Influenced by Johannes Miiller, 245. The cell-theory his 
most important work, 246. Schleiden, his temperament and dis- 
position, 247. Schleiden’s contribution to the cell-theory, 247. 
Errors in his observations and conclusions, 248. Schwann’s 
treatise, 248. Purpose of his researches, 249. Quotations from 
his microscopical researches, 249. Schwann’s part in establish- 
ing the cell-theory more important than that of Schleiden, 250. 
Modification of the cell-theory, 250. Necessity of modifications, 
250. The discovery of protoplasm, and its effect on the cell- 
