Respiration, possessed by Aquatic Mammalia and Birds. 129 



■water, the blood is more florid than under opposite circum- 

 stances; and that after long reposing on land and then betaking 

 themselves to their native element, they in no instance, when 

 they first dive, remain so long under water as in most other 

 occasions. These facts may be obviously accounted for bv 

 supposing, that respiration in these situations being longer 

 continued without interruption than usual, the blood had 

 become more highly oxygenized ; and that hence the brain 

 being temporarily more highly excited, could not at once bear 

 so long a continuance of the venous influence. I have re- 

 peatedly ascertained that the dark venous blood of the seal 

 when exposed to oxygen, as speedily assumes the arterial hue 

 as that of any other animal. 



To a certain extent also, this capacity of suspending respira- 

 tion is under the influence of habit, as we see exemplified by 

 those individuals, even of our own species, engaged in the 

 pearl-fisheries. And moreover, this faculty even in aquatic 

 animals is limited, and differs in the different species ; ibr be- 

 yond a certain period they, like land-animals, are unable to 

 remain under water, I have repeatedly seen seals taken in a 

 net; and when not allowed to come to the surface to breathe, 

 life became extinct generally in less than a quarter of an hour. 

 In this case, it is true, the violent struggling to get loose would 

 naturally abridge the period during which they could remain 

 under water in a tranquil state, which I should believe to be 

 somewhere about twenty minutes. 



The young of the great seal, like the young of the other 

 species of P/ioca, is brought forth on land, and must remain 

 there a month or six weeks before it can live in the water. 

 If before this period it be thrown into the sea, it exhibits as 

 much anxiety and awkwardness as a young dog, and cannot 

 remain longer, without inconvenience, under water. The 

 young of the common seal, on the contrary, follows the mother 

 to the water immediately it is born, and swims and dives with 

 ease and perfection ; a difference so strongly marked and so 

 decidedly established, as in my opinion sufficient to constitute 

 among others a most important feature of specific distinction 

 between them. 



With respect to whales, I have been often assured by in- 

 telligent (irreeniand shipmasters, that they have been fre- 

 quently known to remain upwards of an hour under water; 

 and this also accords with my own observation. The differ- 

 ence therefore in this faculty which we remark in different 

 kinds of aquatic animals, and between these and land-animals, 

 seems more to consist in degree than in kind. 



If a land-bird, as a crow or a pigeon, be thrown into the 

 Nnti Series. Vol.2. No. 8. Au". 1827. S water 



