TEMPERATURE OF THE MOLLUSCA . - In observing the temperature of a single Mollusc, the common oyster, the temperature of the sea being 27°, 8, F.) that of the animal was 27°, 8 also.
It is obvious, therefore, that the differences in the temperature of animals from reptiles inclusively downwards is very inconsiderable. All these animals, indeed, may he united under a single category, and regarded as con stituting a single group characterised by the state or degree of their temperature. The same may also be done with reference to the animals of the two higher classes, Mammalia and Birds, which in point of temperature are so nearly akin to each other.
There are consequently two grand divisions of animals as regards temperature; the one comprising the Mammalia and Birds; the other including Reptiles, Fishes, Insects, Crus taceans, and Molluscs. The first is known under the name of warm-blooded animals, the second under that of cold-blooded animals.
To characterize the first under the view of temperature, the mean of the temperatures of the respective classes which compose it must first be taken. From the experiments of Dr. Davy the mean temperature of Mammalia ap pears to be 4 (101° F. ) that of birds .. 1 F. ) Mean of both classes 25 F.) We may therefore say that the mean tempe rature of warm-blooded animals, including man, surrounded by a moderate external tem perature is in round numbers (104 F.) between the limits of 36° and and 111°, 5 F.), by which we have a scale of dif ference amounting to (about 14° F.).
The other class, that, namely, including the cold-blooded animals, having no peculiar tem perature proper to them, may be characterized in the following manner :—their temperature differs little or not at all from that of the sur rounding media in which they live, when this is at a degree which may be called moderate; so that the differences are either inappreciable, or do not exceed the limits of -I- 4 50 F.). We shall return by-and-by upon this character, which requires development.
General conditions of organization in relation with the production of a greater or less degree heat.
So wide a difference in the heat of the two categories of animals might lead to the pre sumption that there is also a very great dif ference in point of structure. If, indeed, this
relation exists and is easily detected, we may be led to discover the general conditions of organization upon which the production of heat depends. Is there an organization com mon to Mammalia and Birds, distinct and different from that belonging to the other classes of animals ? This question can be an swered in the affirmative : there is a well-marked diversity of organization which distinguishes Mammalia and Birds from all other animals.
I. The most prominent feature of diversity exists in the sanguiferous system, which is divided through its entire extent into two dis tinct parts without direct communication be tween them, the heart presenting a complete median septum, the bloodvessels in like man ner forming two systems of canals, which have also no immediate communication in their trunks.
II. This peculiarity of structure, which is only met with among animals having warm blood, is regularly associated with an organ adapted for aerial respiration. The character which distinguishes this respiratory organ from the one met with among cold-blooded animals, reptiles especially, is this,—that either in itself or its appendices (the air-sacs of birds) it pre sents a much larger extent of surface in relation with the air.
M. Warm-blooded animals are farther dis tinguished from the cold-blooded by important modifications of the digestive canal. 1. The first portion of the apparatus from the mouth to the stomach is much more complex in them; for instance, it presents either a much more perfectly developed dental system, fitted to divide the food, or a sac, as among birds, fitted to macerate the aliment, and cause it to undergo a kind of preparatory digestion before it is passed to the stomach. 2. The stomach is more distinct; either the entrance to and exit from this pouch are better marked, being often provided with a valve, as in the Mam malia, or its structure and form are more spe cial, as we observe it among Birds. 3. The intestinal canal is much longer in the warm than in the cold-blooded tribes.