xviii INTRODUCTION. 



relative importance of Zoological differences as when the local circiimstances con- 

 nected mth them are taken into account. Where I have overlooked facts, or 

 failed in my conclusions concerning them, I must crave that indulgence which is 

 never denied to the honest inquirer even in a field so small as that tlu-oughout 

 which my researches have been prosecuted, — researches which I am well aware 

 can at the best add but an iota to our knowledge, 



" A drop dissevered from the boimdless sea." 



