258 FACULTIES OF BIRDS. 



may fall short of positive proof, they undoubtedly 

 afford much probability to White's opinion, tiiat the 

 hirundines do not. all leave this island in winter*.*' 



Spallanzani saw swallows in October, on the island 

 of Lipari, and he was told that when a warm southerly 

 breeze blows in winter, they are frequently seen 

 skimming along the streets. He thence comes to the 

 same conclusion as the preceding, that they do not pass 

 into Africa at the approach of winter, but remain in 

 the island, and issue from their retreat in warm days 

 in quest of food f. 



As the dormouse, the bat, and other hybernating 

 animals do not appear to have any peculiarity of 

 anatomical structure from which we might account 

 for the circumstance, besides certain depositions of 

 fat J, and a valvular conformation of the veins , the 

 use of which is not well known, we cannot, conse- 

 quently, make any inference upon this point from 

 the anatomical structure of swallows and other migra- 

 tory birds ||. But experiment is no less valuable a 

 test than structure, and experiments respecting the 

 conjectured torpidity of the swallow were tried by 

 Spallanzani, who found that swallows do not appear 

 to suffer by cold at the freezing point ; while at 

 eight or nine degrees below it they manifest uneasi- 

 ness, and at thirteen or fourteen degrees below it they 

 speedily perish. In order to discover the effect of a 

 continued low temperature, Spallanzani confined some 

 swallows in wicker cases covered with waxed silk to 

 keep them dry, burying them in snow with only a 

 hole to admit air. After having been immersed for 

 thirty-five hours, some of them were dead, and others 

 exhibited signs of great weakness, but without any 



* Mag. Nat. Hist. ii. 17. 

 f Travels in the Two Sicilies, iv. 115. 



$ Cuvier, Anat. Comp. iv. 92. 

 Phil. Trans, 1805. |j Bostock, Physiol. ii, 195. 



