TEMPERATURE OF COLD-BLOODED ANIMALS. 333 
animals whose vital actions are the most varied and energetic, 
and in which an interruption to any one of them most 
speedily brings the rest to a stand. The ‘inquiry into the 
amount of heat generated by different animals, and into the 
sources of its production, is one, therefore, of great practical 
importance. 
404. Our knowledge of the heat evolved by the lower In- 
vertebrated animals is very limited; but it is probable that 
in most of them the temperature of the body follows that 
of the element they inhabit, keeping a little above it for a 
time, if it be much lowered. Thus, when water containing 
Animalcules is frozen, they are not at once destroyed; but 
each lives for a time in a small uncongealed space, where the 
fluid seems to be kept from freezing by the ha heat liberated 
_ from its body. The temperature of Earthworms, Leeches, 
Snails, and Slugs, ascertained by introducing a thermometer 
: into the midst of a heap of them, is usually about a degree or 
two above that of the atmosphere ; and they also’ have the 
_ power of resisting for a time the influence of a degree of cold, 
_ which would otherwise immediately freeze their bodies. 
_ -405. In the cold-blooded Vertebrata, also, the heat of the 
_ body is almost entirely dependent upon that of the surround- 
_ingelement. Thus most Fisues are incapable of maintaining 
' a temperature more than two or three degrees higher than 
' that of the water in which they live; and the warmth of 
their bodies consequently rises and falls with that of the sea, 
" Fiver, or lake they may inhabit. There are, however, a few 
_ marine Fishes which have the power of maintaining a tem- 
perature 10 or 12 degrees higher than that of the sea; and 
| these are peculiar for the activity of their circulation, and for 
_ 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 
_ Mediterranean, where there are extensive 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 are 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 
_ deer lakes and rivers is but little altered. Many have the 
e. power of migrating from situations where they might other- 
