CONTENTS. 



CHAPTER IX. 



CUEnEKTS AS A MEANS OF EXTENDING OE HINDERING THE 

 DISTRIBUTION OF SPECIES. 



PAGE 



Migratidh a Condition of Existence in the Lower Animals. Passive 

 Migration. Currpnts and Winds as Means of Distribution. 

 Free Crossing inevitable in Water. Transport of Small 

 Animals. Transition of Forms in Land Animals; for example, 

 in the Philippines. Dispersal of Infusoria. Wagner's Theory 

 of Separation. Some Cases of Resemblance between Animals 

 in Remote Provinces. Conspicuous Effects of Winds. Simi- 

 larity of Fresh-water Mollusca less great than Darwin assumes. 

 American Astacidse. Facility of Transport of Microscopic 

 Bodies. Currents and Winds as limiting the Distribution of 

 Species. Tendency of Currents to Float off the Objects they 

 carry, to each side. Certain Limitations of Distribution in 

 Eastern Asia and Australia 276 



CH.4.PTER X. 



A FEW BEMAEKS AS TO THE INFLUENCE OF OTHER CONDITIONS 

 OF EXISTENCE. 



Gravitation ; Pneumatic Bones. Air in the Body of Fishes. 

 Modifications in the Skull. Pressure of Resistance. Accommo- 

 dation to Pressure. Possible Effects of Electricity 317 



SECTION HI. 

 THE INFLVENCE OF LIVING SVRROUNDINGS. 



CHAPTER XI. 



THE TRANSFORMING INFLUENCE OF LIVING ORGANISMS ON 

 ANIMALS. 



Reciprocal Influences. Parasites on Corals. Mollusca. Sponges. 

 Degeneration of Organs in Parasites. Eiilima in and on » 

 Holothurian. Hybridisation. In Confinement. In a Free State 

 of Nature. Its Effects on Colouring and on Specific Characters 330 



