Xll 



CONTENTS 



CHAPTER III 



An Introduction to the Metazoa 

 i . Germ Cells and Somatic Cells . 



2. Tissues ..... 



3. Organs and Systems of Organs 



4. Reproduction .... 



5. The Forms of Animals . 



PAGK 



73 

 73 

 74 

 76 



79 

 90 



CHAPTER IV 



Phylum Porifera 



1 . Structure of a Simple Sponge — Leucosolenia 



2. Anatomy and Physiology of Grantia 



3. The Fresh-water Sponge Spongilla 



4. Sponges in General 



92 



92 



94 

 98 



99 



CHAPTER V 



Phylum Qelenterata 108 



^- 1. The Fresh-water Polyp — Hydra 108 



2. Class I. Hydrozoa 118 



a, A Colonial Hydrozoon — Obelia, 119; b, Metagene- 

 sis, 122 ; c, A Jellyfish or Medusa — Gonionemus, 122 ; 

 d, Hydroid and Medusa Compared, 124; e, Polymor- 

 phism, 126; f, Reproduction in the Hydrozoa, 127; 

 g, Classification of the Hydrozoa, 128. 



3. Class II. Scyphozoa 129 



a, A Scyphozoan Jellyfish — Aierelia, 129; b, Classifi- 

 cation of the Scyphozoa, 132. 



4. Class III. Anthozoa . . . . . . . 133 



J a, A Sea Anemone — Metridium, 134 ; b, A Coral Polyp, 



137 ; c, Coral Reefs and Atolls, 138 ; d, Classification 

 of the Anthozoa, 139. 



5. Ccelenterates in General 142 



CHAPTER VI 



Phylum Ctenophora 



145 



