262 



LIFE, IN ITS HIGHER FORMS. 



monly takes the temperature of the surrounding water; 

 in some of the swift oceanic Fishes of the Mackerel family, 

 however, such as the Tunny and the Bonito, the blood is 

 found to be 10° higher than the temperature of the sur- 

 face of the sea, even within the Tropics : the flesh of these 

 Fishes is dark and dense. The blood- disks are sometimes 

 circular, sometimes oval. They are larger than those of 

 Mammalia and Birds; smaller than those of Reptiles, 

 and especially than those of Amphibia. 



The irritability of the muscular fibre is considerable, 

 and is long retained. Fishmongers take advantage of this 

 property, to produce rigid muscular contraction, after life 

 has ceased, by transverse cuts and immersion of the 

 muscles in cold water : by this operation, which is called 

 " crimping," the firmness and density of the muscular 

 tissue are increased. 



In our next chapter, we shall enter into some details of 

 the instincts and habits of Fishes, and some other matters 

 connected with the Class, of more popular interest than 

 these structural peculiarities, which, we fear, will prove 

 but a dry morsel to many of our readers. 



