CONTENTS 



PAGE 



III. HOMOLOGY AND ANALOGY 



1. General or Meristic Homology 9 



(a) Bilateral Homology (Homotypy) 



(b) Serial Homology (Homodynamy) 



2. Special Homology (Homogeny, Homophyly) 



3. Homoplasy (False Homology or "Convergence") 



4. Causes of Homology 



(a) The Cause of General Homology . 10 



(b) The Cause of Special Homology 



IV. ORGANIC SYMMETRY 11 



C. MORPHOLOGY OF METAZOA 12 



I. STAGES OF METAZOAN DEVELOPMENT 



1. The Fertilized Egg 14 



2. The Cleavage Stages 



3. The Blastula 



4. The Gastrula 



II. MODIFICATIONS AND COMPLICATIONS OF THE GASTRULA .... I5 



1. Axes and Symmetry 



(a) Protaxonia 



(b) Heteraxonia l6 



2. Mesoderm and Body Cavities 19 



3. Metamerism 20 



III. ORGAN SYSTEMS 23 



1. Integumentary System 



(a) Epidermis 



(b) Dermis 25 



2. Skeletal System 



3. Motor System 28 



(a) Amoeboid movement 



(b) Ciliary Movement 30 



(c) Muscular Movement 32 



vi 



