KK INTRODUCTION. 
upon the causes of such migration. Dr FLEemine, in the 
work before mentioned, clearly demonstrates, that a great 
latitudinal movement from the equator toward the poles 
takes place amongst the feathered tribe, on the approach of 
spring, or immediately previous to the period when nature 
calls for the increase of the species; and that another move- 
ment, the reverse of this, or from the Poles towards the 
Equator, is in force during the autumnal and hyemal months. 
Upon the above great unerring fact, two or three conjec- 
tural observations naturally present themselves. The influ- 
ence of particular climate may be sought for as more conge- 
nial to the production of the race. The progress of vegeta- 
tion, and the consequent display of the insect tribe, may es- 
sentially operate upon the species that look to these sources 
for their supply of food; and, accordingly, we find the arri- 
val of these birds hastened or retarded, as the effects 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 P1.aTE 2.), 
and to offer such a Glossary of Technical Terms (with refe- 
rences to Pirates 1, 2, 3, 4.) as may be found necessary in 
