ENDURANCE OF HEAT AND COLD. 81 



to the mackerel, which, being surface swimmers, 

 have a good respiration, was higher than usually 

 supposed. Thus the bonito was found to possess a 

 temperature of 90 degrees, Fahr., when the sur- 

 rounding medium was 80 5', and may therefore 

 be regarded as an exception to the supposed general 

 rule. Physiologists have shewn that the quantity 

 of respiration is inversely as the degree of muscu- 

 lar irritability. Mr. Yarrell regards it as a law, 

 that those fishes which swim near the surface of the 

 water, have a high standard of respiration, a low 

 degree of muscular irritability, great necessity for 

 oxygen, die almost immediately when removed from 

 the water, and have flesh prone to rapid decompo- 

 sition mackerel, salmon, trout, and herring, being 

 examples of this rule ; while, on the contrary, such 

 as live near the bottom of the water, have a low 

 standard of respiration, a high degree of muscular 

 irritability, less necessity for oxygen, a more en- 

 during power of life in open air, and flesh which 

 keeps fresh for several days. Of this second rule, 

 carp, tench, eels, and the various kinds of skate 

 and flat-fish, may be mentioned as examples. 



Whatever may be the physical temperature of 

 fishes, there is nothing in their history more re- 

 markable than their power of enduring the extremes 

 of heat and cold. The breeding powers of that 

 brilliant species of Chinese carp, commonly called 

 the gold-fish, are greatly accelerated by water kept 

 at a constant temperature of 80 Fahr. ; yet Mr. 

 Hoste, a naturalist of Vienna, has seen that species 

 recover freely after being frozen up in ice. Fishes 



