IT PREFACE. 



Dragons and the Flying Frog. Even in the fishes 

 and the molluscs we find examples of Trespassers on 

 the domain of air, such as the Flying Fishes, Flying 

 Gurnards, and Flying Squids. 



Lastly, we find that some of the fishes, such as 

 the Climbing Perch, and several marine Crustacea, 

 such as the Land Crabs, the Kobber Crabs, and the 

 Hermit Crabs, are able to leave the water and to 

 trespass on the domain of the mammalia. 



It has been my endeavour, in the course of this 

 work, to show how simple, and yet how effectual, 

 are the modifications of structure by which a mammal, 

 ordinarily an inhabitant of earth, is enabled to tres- 

 pass upon the domains of the Fishes and the Birds 

 a bird or reptile to trespass upon the realm which 

 belongs to the Fishes, and a fish to trespass upon 

 that of the Mammal. 



