32(5 PHILOSOPHICAL TBANSACTIONS. [aNNO I766 



From these considerations it appears, beyond contradiction, that the phocae of 

 every kind are under an absolute necessity of niaking the land their principal re- 

 sidence ; but there is another very convincing argument why they reside on shore 

 the greatest part of their time, and that is, that the flesh of these creatures is 

 analogous to that of other land animals ; and therefoi^, by over-long maceration, 

 added to the fatigue of chacing their prey, they would s-ufFer such a relaxation aa 

 would destroy them. It is well known that animals, which have lain long under 

 water, are reduced to a very lax and even putrid state ; and the phoca must bask 

 in the air on shore ; for while the solids are at rest, they acquire their former 

 degree of tension, and the vigour of the animal is restored ; and while he has 

 an uninterrupted placid respiration, his blood is refreshed by the new supply of 

 air, as explained above, and he is rendered fit for his next cruise : for action 

 wastes the most exalted fluids of the body, more or less, according to its dura- 

 tion and violence ; and the restorative rest must continue a longer or shorter time, 

 according to the quantity of the previous fatigue. 



Let us now examine by what power these animals are capable of remaining 

 longer under water than land animals. All these have the oval hole open, be- 

 tween the right and left auricles of the heart, and in many the canalis arteriosus 

 also: and while the phoca remains under water, which he may continue an hour 

 or two more or less, his respiration is stopped, and the blood, not finding the 

 passage through the pulmonary artery free, rushes through the hole from the 

 right to the left auricle, and partly through the arterial canal, being a short pas- 

 sage to the aorta, and thence to every part of the body, maintaining the circu- 

 lation : but, on rising to come ashore, the blood finds its passage again through 

 the lungs the moment he respires. 



Thus the foetus in utero, during his confinement, having the lungs compressed, 

 and consequently the pulmonary arteries and veins impervious, h^s the circulation 

 of the blood carried on through the oval hole and the arterial canal ; now so far 

 the phoca in the water and the foetus in utero are analogous ; but they differ in 

 other material circumstances : one is, that the foetus, having never respired, re- 

 mains sufficiently nourished by the maternal blood circulating through him, and 

 continues to grow till the time of his birth, without any want of respiration 

 during 9 months confinement; the phoca, having respired the moment of his 

 birth, cannot live very long without it, for the reasons given before; and this 

 hole and canal would be closed in them, as it is in land animals, if the dam did 

 not, very soon after the birth of the cub, carry him into the water to teach him, 

 so very frequently; by which practice these passages are kept open during life; 

 otherwise they would not be capable of attaining the food designed for them by 

 Providence. 



Another difference is, that the phoca, as before said, would be relaxed by 



