CONTENTS. 



V. Histology 



1. The Ectoderm .... 



General Structure of the Ectoderm . 



Palpocils .... 



Fibrillated Tissue 



Umbrella of Medusa 



Nematopliores .... 



Thread-cells . . . • 



2. The Endoderm .... 



Cellular Structure of Endoderm. — Contents of the Cells 

 Canaliculation of Eudoderra 

 Endoderm of Tentacles 



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PHYSIOLOGY OF THE HYDROIDA 



1. Digestion .... 



2. Circulation, Nutrition, and Respiration 



3. Secretion . . • ■ 



4. ContractOity . . . • 



.5. Sensation . . . • 



The Ocellus 

 The Lithocyst 

 Touch .... 



6. Phosphorescence 



7. Reproduction 



a. Sexual Reproduction. — Generation 



Comparison of the Sexes in the Hydroida 

 Origin of the Generative Elements . 



h. Non-Sexual Reproduction . 

 Gemmation 

 Fission 



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