Ixviii 
INTRODUCTION. 
Why do they, for so long a season, exert themselves in such extraordinary 
preparations, if their journey terminate in a contiguous stream ? Why 
such precnings — such circlings — such trials of their wings ? Where can 
they discover beneath the water a well-gTiarded retreat, in which they may 
repose in security, evade the attacks of enemies, and defy the rapidity of 
the stream ? If nature intended them as an anomaly to her laws, would 
she net have provided them with ditferent organs from the rest of the 
feathered creation ? Would not their'plumage be impermeable by humi- 
dity, and their bodies indestructible by the want of vital air ? Has any 
one yet discovered this water-proof vesture, these extraordinary organs, 
these unusual provisions of nature, in the Swallow tribes ? Has any one 
marked the Swallow torpid in vacuo, or submersed it in water, and seen it 
recover, after the lapse of a few days only, its animation ? Does it respire 
while submersed ? Has it then lost its animal heat, which can only be 
kept up by respiration ? If it do not possess this extraordinary conforma- 
tion, if its organs be not dissimilar from those of other land birds ; if it 
respire in torpidity, and retain its animal heat ; if its plumage be not im- 
pervious to humidity, it could not exist in a watery grave ; it would die 
when the frozen surface precluded the access of the air ; it would fail a 
sacrifice to the action of the water, be suffocated by its pressure, or 
destroyed by its penetration. True it is, that were wm unacquainted with 
the habits of the Water- ouzel, vre should not readily give credence to an 
assertion of its diving for food; for, without the web, the characteristic of 
water-fowl, w’e see it sink into the stream. On a cursory inspection, the 
Swallow appears ecprally as well fitted for submersion ; but a closer exami- 
nation soon convinces us, that the one has been clothed in a thick, impene- 
trable plumage to resist the entrance of humidity, although its stay beneath 
the water is but momentary, while to the other nature has denied an im- 
pervious clothing, xill the arguments for the doctrine of submersion are 
deductions from a few solitary, most probably deceitful, instances, while the 
advocates for the migration of the Swallow adduce a forcible train of 
facts, w^hich readily convince the unbiassed mind, d'he general nature of 
