CONTENTS. 



T±CTS 



Preface, 3 



Introduction : The General Principles of Biology, . 9 



Chap. I. — The Distinctive Characters of Animals, . . . .44 



11. — The Protozoa, 73 



III. — The Porifera and the Coelenterata, 102 



lY. — The Turbellaria, the Rotifera, the Trematoda, and the 



Cestoidea, 15Y 



V. — The Hirudinea, the Oligoch^ta, the Polych^ta, the 



Gephyrea, 189 



YI. — The Arthropod a, 219 



YII. — The Air-breathing Arthropoda, 320 



YIII. — The Polyzoa, the Brachiopoda, and the Mollusca, . . 389 



IX. — The Echinodermata, 466 



X. — The Tunicata or Ascidioida, 510 



XI. — The Peripatidea, the Myzostomata, the Enteropneusta, 

 the Ch^tognatha, the Nematoidea, the Physemaria, 



THE ACANTHOCEPHALA, AND THE DiCYEMIDA, . . . 534 



XII. — The Taxonomy of Invertebrated Animals, . . . .561 

 Index, 589 



