xii CONTENTS 



CHAPTER PAGE 



Adaptive Structural Species Characters 348 



The Bird as an Example of Fitness for Habitat 349 



Special Types of Adaptive Structures 352 



The Gas Bladder of Fishes 352 



Electric Organs 353 



Defense Mechanisms 354 



Luminescence in A.nimals 356 

 The Class Insecta as an Example of Divergence within a 



Related Group 357 



Insect Types 358 



Inheritable Functional Characters 363 



The Tapeworm as an Example of Limited Habitat 364 



Individual Modifications That Are Adaptive 366 



The Nature of Response to Environment 366 



Trembley's Experiment with Hydra 368 



Behavior 370 



Phototropism 373 



Graviotropism 373 



Galvanotropism 373 



Stereotropism 374 



Thermotropism 374 



Chemotropism 375 



Other Responses and Behavior 375 



Animal Communities 377 



Social Life within the Species 384 



XI. The History of Animal Life and Its Interpretation 387 



Fundamental Considerations 387 



Organic Evolution 388 



The Mechanism of Evolution 388 



Lamarck 389 



Darwin 390 



Weismann 392 



De Vries 392 



Comparison of the Chief Theories of the Mechanism of 



Evolution 393 



Modern Views 393 



Orthogenesis 395 



Limitations of the Theories 395 



The Evidence from Paleontology 396 



Ancestry of Birds 403 



Ancestry of Man 404 



