CONTENTS. IX 



CHAPTER VI. 



THE INFLUENCE OF A STILL ATMOSPHERE. 



PAGE 



Action of the Lungs. Composition of Air. Tracheae in Insects. 

 Resistance to a Dry Atmosphere. Desert Snails. Effects of a 

 Saturated Atmosphere. Land Leeches. Land Planarians. 

 Mollusca. Accommodation of Water-breathers to breathing Air. 

 Amphibious Fishes (Gofriidte). Amphibious Mollusca (.!>- 

 pullaria). Land Crabs (Birgus latro). Transformation of 

 the Branchial Cavity into a Lung 178 



CHAPTER VII. 



THE INFLUENCE OF WATER IN MOTION*. 



Presence of Salts in Fresh Water. The Mechanical Factor. Re- 

 sistance to Currents. Sedentary Animals. Floating and 

 Swimming Animals. Swimming Organs. Clinging Power of 

 Mollusca. Mechanical Effects of Currents. Erosion of Shells. 

 Corals acted on by Currents produced by Crabs, which form 

 Galls, or Funnels. General Structure of Massive Corals 

 (Puriteg). Process of Growth ; Formation of Reefs as affected 

 by Marine Currents 200 



CHAPTER VIII. 



THE INFLUENCE OF WATER IN MOTION (continued). 



The Formation of the Coral Reefs of the Pelew Islands. The 

 Views of Dana and of Darwin disputed. Barrier Reefs and 

 Fringing Reefs. General Form and Structure of the Pelew 

 Reefs. Kriangle. Blocks of Dead Coral. Artificial Canal. 

 Kossol ; the Depth of the Reef. Babelthuap ; Slope of the 

 Eastern Reef. Submarine Ridge of Elevations. Theory of 

 Subsidence as explaining the Origin of the Pelew Reefs and 

 Islands. Objections. Co-operation of Currents. Sections of 

 the Reef. Geological Structure partly Volcanic. Evidences 

 of Upheaval. An Attempt to explain the Structure of these 

 Reefs by Upheaval. Possible Objections answered. Pourtales 

 Plateau in the West Indian Sea. Mixture of Forms and 

 Species 230 



