See ANAS, Ornithology Index.

This fowl is furnished with a peculiar structure of vessels about the heart, which enables it to live a considerable time under water, as is necessary for it in diving. This made Mr Boyle think it a more proper subject for experiments with the air-pump, than any other bird. A full-grown duck, being put into the receiver of an air-pump, of which she filled one-third part, and the air exhausted, the creature seemed to bear it better for the first moments than a hen or other such fowl; but, after about a minute, she showed great signs of uneasiness, and in less than two minutes her head fell down, and she appeared dying, till revived by the admission of the air. Thus, whatever facility of diving this and other water fowl may have, it does not appear that they can subsist without air for respiration, any longer than other animals. A young callow duck was afterwards tried in the same manner, and with the same success, being reduced very near death in less than two minutes. But it is observable, that both birds swelled very much in pumping out the air, so that they appeared greatly larger to the spectators, especially about the crop: it not being intended that any water fowl should live in an exceeding rarefied air, but only be able to continue occasionally some time under water. Nature, though she has provided them with the means of this, hath done nothing for them in regard to the other.

The strongest instance of these creatures being calculated to live almost in any situation, we have in the accounts of the blind ducks in the Zirchitzer lake in Carniola. It is supposed that this lake communicates with another lake under ground in the mountain Savornic, and fills or empties itself according to the fulness or emptiness of that lake; the water of the upper lake running off, and that in vast quantities, by holes in the bottom. The ducks which are here always in great numbers, are often carried down along with the water, and forced into the subterraneous lake to which it retires. In this unnatural habitation many of these creatures undoubtedly perish, but some remain alive. They become blind, and lose all their feathers; and in the next filling of the lake, both they and vast numbers of fish are thrown up with the water. At this time they are fat, but make a strange appearance in their naked state, and are easily caught, by reason of their want of flight. In about a fortnight they recover their flight and feathers; and are then of the size of a common wild duck, but of a black colour, with a white spot on their forehead. When opened, on being taken at their first coming up in their blind state, their stomachs are found full of small fishes, and somewhat resembling weeds. From this it seems that they cannot be absolutely blind: but that the degree of light to which they have been accustomed in their subterraneous habitation, is sufficient to enable them to procure food for themselves; and their blindness, on coming again to open daylight, is no other than that of a man who has been long in the dark, on having in an instant a large blaze of candles set under his eyes.