. Animal physiology. Physiology, Comparative; Physiology, Comparative. TEMPERATURE OP COLD-BLOODED ANIMALS. 311 degrees higher than that of the sea ; and these are peculiar for the activity of their circulation, and the deep colour of their blood, which possesses red particles (§. 229) enough to give to the muscles a dark red colour like that of meat. The Thunny, a fish which abounds in the Medi- terranean, where there are exten- sive fisheries for it, is one of this group.—It is to be remembered that the animals of this class are less liable to suffer from seasonal alternations of temperature
. Animal physiology. Physiology, Comparative; Physiology, Comparative. TEMPERATURE OP COLD-BLOODED ANIMALS. 311 degrees higher than that of the sea ; and these are peculiar for the activity of their circulation, and the deep colour of their blood, which possesses red particles (§. 229) enough to give to the muscles a dark red colour like that of meat. The Thunny, a fish which abounds in the Medi- terranean, where there are exten- sive fisheries for it, is one of this group.—It is to be remembered that the animals of this class are less liable to suffer from seasonal alternations of temperature, than those which inhabit the air. In climates subject to the greatest atmospheric changes, the heat of the sea is comparatively uniform throughout the year, and that of deep lakes and rivers is but little altered. Many have the power of migrating from situations where they might otherwise have suffered from cold, into deep waters; and those species which are confined to shallow lakes and ponds, and which are thus liable to be frozen during the winter, are frequently en- dowed with sufficient tenacity of life, to enable them to recover after a process which is fatal to animals much lower in the scale. Fishes are occasionally found imbedded in the ice of the Arctic seas; and some of these have been known to revive when thawed. 406. In Reptiles, the power of maintaining an uniform temperature is somewhat greater ; being especially shown when the external temperature is reduced very low. Thus when the air is between 60 and 70 degrees, the body of a Reptile will be nearly of the same heat; but when the air is between 40 and 50 degrees, it may be several degrees higher. Frogs and other aquatic Reptiles have a remarkable power of sustaining a tem- perature above that of freezing, when the water around is not only congealed, but is cooled down far below the freezing-point. Thus in ice of 21 degrees, the body of an edible frog has been found to be 37^ degrees; and even in ice of 9
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