xxvi Contents 



CHAPTER PAGE 



(c) Re/lections on a promorpholorfy of germ cells beyond the 

 limits of visibility, 



IX. Organisms Consistixg of Oxe Cell 237 



A. Ackdt form and structure. Remarks on the conception 



of the cell as an elementary organism, 221. Comparison of 

 the structure of a single cell with that of organisms composed 

 of m,any cells, 230: (a) Comparison of certain ciliates and 

 metazoans, 232; (b) Comparison of a radiolarian and a jelly- 

 fish, 235; (c) Comparison of the shell of a rhizopod and a 

 nautilus, 237. The unjustifiable conception that unicellular 

 organisms can have no tissues, 240. True organs in some pro- 

 tozoans, 242. A true nervous system probably present in some 

 protozoa, 244- ^ more critical examination of the term "or- 

 gan," 245. More detailed examination of the anatomy of 

 higher protozoa, 249. The fiction of structureless organisms, 

 256. The structure of bacteria, 257: (a) Membrane and sur- 

 face structures, 257; (6) Structure of inner portion, 260; (c) 

 The question of a nucleus in bacteria, 261. Bacteria un- 

 doubted organisms whether "true cells" or not, 263. B. De- 

 velopment, 267. False conceptions about development in pro- 

 tozoa, 267. Misuse of the term "ontogeny," 271. Development 

 of Stentor as an example of protozoan ontogeny, 272. The 

 terms "embryology" and "ontogeny" inevitably used by irv- 

 vestigators of protozoan reproduction, 277. 



X. History of the Attempt to Subordinate the Protista to the 



Cell-theory 280 



Clash between Ehrenberg and Dujardin a special case of the 

 ■ conflict between organismal and elementalist conceptions, 280. ' 

 Modern opposition to the e^ort to make protista conform to 

 cellular elem,entalism, 286: (a) Position of Friederich Stein, 

 286; (6) Position of Huxley, R. Hertwig and others, 288. 

 General conclusions from examination of knowledge and views 

 as to the nature of uni- and multicellular organisms, 291. 



B. The Production of Individuals by Other Individuals 



XI. The Nature of Heredity and the Problem of its Mechan- 



ism 305 



Heredity the chief present-day stronghold of biological ele- 



