7 



CONTENTS 



PAGE 



Preface . . . i. v 



CHAPTER 



I. General Directions 1 



II. External Characteristics 4 



Key for Determination of Species 4 



Animal Form 6 



Imaginary Planes and Axes 6 



Symmetry 7 



III. The Eespiratory System 11 



The Mouth and Pharyngeal Cavity 11 



Visceral Arches 12 



IV. The Coelom, Digestive System, and Mesenteries . . 14 



The Coelom and Its Walls 14 



The Pleuroperitoneal Viscera 15 



The Digestive Tract and Derivatives 15 



The Spleen 18 



The Mesenteries .............. 18 



V. The Urogenital System 19 



The Female • . 20 



The Male 22 



VI. The Circulatory System 24 



The Pericardial Cavity and the Heart 24 



The Venous System 26 



The Arterial System and the Heart 30 



ix 



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