408 MR. R. BROWN ON THE SEALS OF GREENLAND. [JuDC 2.5, 



fiud the foramen ovale unenclosed to within a line of the aorta. 

 That of Blumenbach and Houston has been also brought forward, 

 viz. that venous sinuses are to be found in the liver and surrounduig 

 parts, and that the large veins have been observed to be enlarged and 

 tortuous ; these have been supposed to act as reservoirs for the re- 

 turning venous blood while the animal is diving under the water. 

 But this theory carries inconsistency in itself. The venous system 

 on the whole, and not in any particular part, unless in the vena cava, 

 from the pressure excited on its walls, is greatly enlarged ; but this 

 arises from the great quantity of blood these animals jiossess. But, 

 even supposing these venous sinuses and that the animal will re- 

 main below the surface for twenty or twenty-five minutes (though I 

 must assert that I never saw them remain longer below the surface 

 than fifteen minutes, and from five to eight is the common time), 

 are these sinuses large enough to contain the full quantity of blood 

 that may return in that period from the capillary system ? The 

 reply is certainly in the negative. Does the heart's action diminish 

 in rapidity or come to a full stop ? in that case there would be no 

 need of these sinuses. What, then, are the uses of them ? 



After a very careful examination, Dr. Wallace informs me that he 

 never could find them, in all the Seals which he examined. He cer- 

 tainly remarked the dilated condition of the veins, but referred this 

 to a physiological cause, viz. the pressure of the superincumbent 

 column of blood. He believes that their power of remaining so 

 long below the surface of the water is to be referred to a cause phy- 

 siological, and not structural. Their expertness in swimming is not 

 possessed from birth, but only developed from an innate instinct. 

 He has often watched young Seals taking the water at first in smooth 

 pools among the ice, and then swimming slowly and quietly about 

 in the still floe-water — then gradually taking the water, staying 

 below the water at first but a sliort time, gradually lengthening 

 their stay until they had acquired the faculty of remaining the 

 usual time beneath the surface. Dr. Wallace, then, thinks that 

 this faculty is owing to a cause more physiological than anatomical, 

 and that the explanation he has given, coupled with the enormous 

 quantity of blood which the Seal contains, will account for their 

 power of remaining beneath the water. As I have not examined 

 the anatomy of the i'innipedia with this object iu view, I cannot 

 presume to give an opinion on the matter ; in the Narwhal and 

 other Cetacea which I examined, the extensive venous plexus about 

 the vertebral column seemed to explain the possession of this power of 

 tempcrary subaquatic existence. The flesh of the Seal is quite black, 

 from the enormous quantity of venous blood it is impregnated with ; 

 but if exposed to the air or steeped in water, it acquires the usual 

 arterial rosy hue. The flesh of young seals which have not yet taken 

 the water is, on the contrary, quite red. 



3. Habits and Instincts of Seals in general. 

 Thev spend a con.<iderable part of their time in feeding, but they 



