CONTENTS 



CHAPTER PAGE 



I. THE LIFE OF THE SIMPLEST ANIMALS 1 



The simplest animals, or Protozoa, 1. The animal cell, 2. 

 What the primitive cell can do, 5. Amoeba, 5. Paramcecium, 9. 

 Vorticella, 12. Marine Protozoa, 15. Globigerinas and Eadio- 

 laria, 16. Antiquity of the Protozoa, 20. The primitive form, 

 20. The primitive but successful life, 21. 



II. THE LIFE OF THE SLIGHTLY COMPLEX ANIMALS . . .94 



Colonial Protozoa, 24. Gonium, 25. Pandorina, 26. Eudo- 

 rina, 27. Volvox, 28. Steps toward complexity, 30. Individual 

 or colony, 31. Sponges, 32. Polyps, corals, and jelly-fishes, 37. 

 Hydra, 37. Differentiation of the body cells, 41. Medusae or 

 jelly-fishes, 41. Corals, 43. Colonial jelly-fishes, 45. Increase 

 in the degree of complexity, 48. 



III. THE MULTIPLICATION OF ANIMALS AND SEX ... 50 



All life from life, 50. Spontaneous generation, 51. The 

 simplest method of multiplication, 53. Slightly complex methods 

 of multiplication, 54. Differentiation of the reproductive cells, 55. 

 Sex, or male and female, 57. The object of sex, 57. Sex di- 

 morphism, 58. The number of young, 61 . 



IV. FUNCTION AND STRUCTURE 63 



Organs and functions, 63. Differentiation of structure, 64. 

 Anatomy and physiology, 64. -The animal body a machine, 65. 

 The specialization of organs, 66. The alimentary canal, 66. 

 Stable and variable characteristics of an organ, 73. Stable and 

 variable characteristics of the alimentary canal, 73. The mutual 

 relation of function and structure, 77. 



V. THE LIFE CYCLE 78 



Birth, growth and development, and death, 78. Life cycle of 

 simplest animals, 78. The egg, 79. Embryonic and post-em- 

 bryonic development, 80. Continuity of development, 83. De- 

 velopment after the gastrula stage, 84. Divergence of develop- 



