XX INTRODUCTION. 



congenial to tlie production of the race. The progress of 

 vegetation, and the consequent display of the insect tribe, 

 may essentially operate upon the species that look to these 

 sources for their supply of food ; and, accordingly, we find 

 the arrival of these birds hastened or retarded, as the ef- 

 fects of an early or late spring would suggest. During the 

 time that insects are in the dormant and concealed state in 

 one latitude, they may be in the active and requisite state 

 in another, and an equalization of destruction in that tribe 

 will doubtless have been ordained by Providence for the 

 wisest purposes ; at the same time that the feathered race 

 themselves present to the inhabitants of different countries 

 an important periodical object either of food or economical 

 utility. 



I shall now proceed to give an explanation of the Plumage 

 of Birds, (with references to the outline etching on Plate II), 

 and to offer such a Glossary of Technical Terms (with re- 

 ferences to Plates 1, 2, 3, 4.) as may be found necessary in 

 the course of the work. These plates are also intended to 

 exhibit the leading principles of generic distinction, in a 

 regular series ; as a reference to the " Types of the Genera" 

 (hereafter given) will demonstrate. 



Let me here mention, that the Nomenclature of Colours 

 adopted in the present work, is that of Werner, as exhibited 

 and improved by Mr Syme of Edinburgh, in a work which 

 ought to be in the hands of every Amateur of Natural His- 

 tory. 



