328 On the Temperature of Fislie$. 



tion of some of the peculiarities of these fish may help to dimi- 

 nish this difficulty, which I have little doubt will be removed 

 entirely when we are better acquainted with their structure, and 

 better acquainted with all the sources of animal heat. 



The most important peculiarities are, I believe, chiefly the 

 following : — A large and powerful heart ; abundance of blood ; 

 large gills ; and a very large apparatus of branchial nerves ; — all 

 which may be considered as concerned, either directly or indirect- 

 ly, in the generation of heat : and the circumstances for its pre- 

 servation are hardly less remarkable, as the manner in which the 

 gills are defended by peculiarly strong opercula, abounding in 

 fatty matter, and the deep situation of the principal bloodvessels, 

 surrounded by thick muscles, and in addition, the aorta sur- 

 rounded by the principal abdominal viscera, the kidneys, sto- 

 mach, and liver. Moreover, the habits of these fish may, in 

 some measure, contribute to their high temperature. They are 

 frequently to be seen near the surface, and seem to have a de- 

 light in springing into the atmosphere. Aristotle, speaking of 

 the tunny, says, of all fish it most enjoys warmth, and on that 

 account swims near the surface, and frequents sandy shores. I 

 quote from the old Latin translation of Theodore Gaza. " Thun- 

 m omnium maxime piscium gaudent tepore et ob earn rem are- 

 nam et littora adeunt ; per summa etiam maris innatant, quo 

 teporis potiantur * — confounding, as I believe in this instance 

 he has done, a fondness for warmth, with the habits connected 

 with its production. In this enumeration of circumstances which 

 may contribute to the high temperature of these fish, both as 

 regards its generation and preservation, I have intentionally been 

 very general. In the present state of our knowledge, I appre- 

 hend it would be useless to be more minute. It is not impro- 

 bable that these fish may possess means for generating heat pe- 

 culiar to themselves, and of which at present we have no ade- 

 quate idea; and the situation of the kidneys, of which a consi- 

 derable portion is even higher than the stomach, and posterior 

 to the gills, of large size, and abounding in blood, and well sup- 

 plied with nerves, would lead to the conjecture that these or- 

 gans, in the function of imparting heat, may possibly act a part. 



* De Hist. Animal, lib. viii. cap. 19. 



