BIRDS IN GENERAL. 31 



be, their retreat into old walls is too well authen- 

 ticated to remain a doubt at present. The diffi- 

 culty, therefore, is to account for this difference 

 in these . animals thus variously preparing to en- 

 counter the winter. It was supposed that in 

 some of them the blood might lose its motion by 

 the cold, and that thus they were rendered tor- 

 pid by the severity of the season ; but M. Buffon 

 having placed many of this tribe in an ice-house, 

 found that the same cold by which their blood 

 was congealed was fatal to the animal: it re- 

 mains, therefore, a doubt to this hour, whether 

 there may not be a species of swallows, to all 

 external appearance like the rest, but differently 

 formed within, so as to fit them for a state of 

 insensibility during the winter here. It was sug- 

 gested, indeed, that the swallows found thus tor- 

 pid were such only as were too weak to under- 

 take the migration, or were hatched too late to 

 join the general convoy ; but it was upon these 

 that M. Buffon tried his experiment ; it was these 

 that died under the operation. 



Thus there are some birds which by migrating 

 make a habitation of every part of the earth ; but 

 in general every climate has birds peculiar to it- 

 self. The feathered inhabitants of the temperate 

 zone are but little remarkable for the beauty of 

 their plumage ; but then the smaller kinds make 

 up for this defect by the melody of their voices. 

 The birds of the torrid zone are very bright and 

 vivid in their colours, but they have screaming 

 voices, or are totally silent. The frigid zone, on 

 the other hand, where the seas abound with fish, 



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