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126 Proceedings of Learned Societies. 



appearance and return of birds has been ascribed to hybernation, 

 but of this Dr. Jenner never witnessed an instance ; nor could he 

 ever obtain any satisfactory evidence of it. When birds appear 

 for the season, they are never in the emaciated and weakened 

 state attended with loss of fat, which characterizes hybernating 

 quadrupeds when they quit their retreats ; the birds, on the con- 

 trary, are quite vigorous, and as active as at any period. With 

 regard to the supposed immersion of birds in ponds and rivers for 

 the winter, Dr. J. remarked, that their respiratory organs are very 

 similar in structure to those of quadrupeds, and are no better 

 adapted for performing their functions under Avater. He took a 

 Swift, about the 10th of August, or on the eve of its departure, 

 and held it under water, when it died in two minutes. It has been 

 conjectured, that repeated alternate immersions and emersions 

 might have the effect of altering the corresponding action of the 

 heart and lungs ; but though Swifts and Martins, it was observed, 

 in reply to this conjecture, frequently splash in the water over 

 which they are skimming, yet they never immerge themselves in 

 it, and indeed if they were to do so, their wings would become so 

 wet as to prevent their flying. The common Duck, when pursued 

 and forced to dive repeatedly, by a water-dog, arrives at the sur- 

 face again much exhausted ; as is likewise the case with Grebes 

 and Auks, after repeated diving. Dr. Jenner had been in the 

 habit of receiving Newfoundland Dogs from that country, and had 

 ascertained that they never continued under water for more than 

 thirty seconds, and even then seemed confused when they came 

 up. It had been asserted that negro and other divers remained 

 under water several minutes ; but Dr. J. conceived this assertion to 

 be grounded only on a vague guess, and that the time was not 

 accurately measured. 



The next division of the paper related to the remarkable effect 

 of instinct in birds, of their returning to build on the same spot 

 for many successive seasons. The author took twelve Swifts from 

 their nests in a barn, indelibly marked them all, by taking off two 

 claws from one foot of each, and then set them at liberty. Some 

 of them were caught again on the same spot, at the expiration of a 

 year, and others after two years had elapsed : (hey were not at- 



