Dr. Jenner on the Migration of Birds. 55 



The late Doctor Beddoes has thrown out a supposition, that 

 by frequent immersion in water, the association between the 

 movements of the heart and lungs might perhaps be destroy- 

 ed, and that an animal might be inured to live commodiously 

 for any time under water. As this will probably give new vi- 

 gour to the languid system of the advocates for the submer- 

 sion of birds, I think it incumbent upon me to mention it. 



Though we frequently see the swallow and the martin 

 sprinkle and splash themselves as they glide over the surfaces 

 of ponds and rivers, yet we never see them dip under for a 

 single moment ; indeed a few plunges would so moisten their 

 wings as to prevent their flying, and we should see them oc- 

 casionally in this disordered state fluttering on the shore. If 

 they went to the sea side, and got beyond the reach of the eye 

 to inure themselves to this element, how could they return, 

 divested as they must be either of the means of swimming or 

 flying ? Whoever has observed the common tame duck driven 

 to the necessity of repeatedly diving from the pursuit of a 

 water-dog, must have noticed how exhausted it rises to the 

 surface of the water after a short period of submersion, and 

 how incapable it is of flying, in consequence of the soaking of 

 its wings. The same may be said of birds more in the habit 

 of diving, the grebes and divers. When entangled in a net 

 they soon perish, or when they happen to dive under ice that 

 may chance to overspread a pond ; no uncommon place of 

 resort for some of the smaller species of grebes. 



I have always been much attached to that faithful animal, 

 the Newfoundland dog, and have often procured from that 

 country those dogs that had been much accustomed to diving, 

 and which had been kept to the practice ; yet I never ob- 

 served that any of them attained by habit the power of remain- 

 ing under water longer than thirty seconds, and even then, on 

 rising to the surface, they appeared confused. Negroes and 

 other men who have been employed in seeking among sunken 

 rocks the hidden treasures of the deep, are said to have ac- 

 quired a habit of remaining some minutes under water ; but 

 the time was probably measured by a rude guess, and not by 

 a stop-watch. 



Having thus called the attention of the Society to such state- 

 ments as give support to the fact of migration, and having 

 also endeavoured to controvert the notion of an hibernating 

 system, I beg to draw their attention to what 1 conceive to be 

 the true cause of migration. 



At the coming on of spring we observe our more domestic- 

 birds, those that approach our houses, and are most familiar 

 to us, assuming new habits, The voice, gesticulation, and the 



attachment 



