xii CONTENTS 



PACB 



PHYLUM PROTOZOA continued. 



Class Y. Infusoria . ... .79 



1. Example of the Class Paramoscium caudtttimi . . 79 



2. Classification and General Organisation . . 82 

 Systematic Position of the Example . . 82 

 Further Remarks on the Protozoa . 92 



SECTION III 



PHYLUM AND CLASS PORIFERA .96 



1. Example of the Class Si/co)i gelatinosum . . .96 



2. Distinctive Characters and Classification ... .102 

 Systematic Position of the Example ... . 103 



3. General Organisation 105 



SECTION IV 



PHYLUM CCELENTERATA . . . 118 



Class I. Hydrozoa . . . 118 



1. Example of the Class Obelin . ... . . 118 



2. General Structure and Classification . . . 13O 

 Systematic Position of the Example ... . 132 



3. Additional Remarks ... . . . 155 



Class II. Scyphozoa . . . 156 



1. Example of the Class Aurelia aiirita . . . . 156 



2. General Structure and Classification .... . 163 

 Systematic Position of the Example .... . 164 



3. Additional Remarks . . . . 171 

 Class III. Actinozoa . . . . . 172 



1. Example of the Class Tealia crassicornis . . . 172 



2. Distinctive Characters and Classification ... . 180 

 Systematic Position of the Example . . . . 183 



3. General Organisation . ... 183 

 Class IV. Ctenophora . . .198 



1. Example of the Class Hormiphora plnmosa . . . 198 



2. Distinctive Characters and Classification ........ 207 



Systematic Position of the Example . . . . 208 



3. General Organisation . 209 



Appendix to Ctenophora Ct'enoplana and Codoplana . . . 212 



The Relationships of the Ccelenterata 213 



Appendix to the Ccelenterata . 216 



The Mesozoa . .... 216 



Salinella . . . 219 



Trichoplax . . 220 



SECTION V 



PHYLUM PLATYHELMINTHES . . .... . 221 



1. Examples of the Phylum . . 222 



i. Plnnaria or Dendroccelnm .... . 222 



ii. Distomum hepaticum . . 226 



iii. Ta'nia sulium 231 



