140 
PECULIAR ORGANIZATIONS. 
made to ascend and descend, upon the like principle; name¬ 
ly, by introducing into the inside of it an air-vessel, which 
by its contraction would diminish, and by its distension en¬ 
large, the bulk of the machine itself, and thus render it 
specifically heavier, or specifically lighter, than the water 
which surrounds it. Suppose this to be done, and the ar¬ 
tist to solicit a patent for his invention: the inspectors of 
the model, whatever they might think of the use or value 
of the contrivance, could, by no possibility, entertain a 
question in their minds, whether it were a contrivance or 
not. No reason has ever been assigned—no reason can be 
assigned, why the conclusion is not as certain in the fish 
as it is in the machine; why the argument is not as firm in 
one case as the other. 
It would be very worthy of inquiry, if it were possible to 
discover, by what method an animal, which lives constantly 
in water, is able to supply a repository of air. The ex 
pedient, whatever it be, forms part, and perhaps the most 
curious part, of the provision.* Nothing similar to the air- 
bladder, is found in land-animals; and a life in the water 
has no natural tendency to produce a bag of air. Nothing 
can be farther from an acquired organization than this is. 
These examples mark the attention of the Creator to 
the three great kingdoms of his animal creation, and to their 
constitution as such.—The example which stands next in 
point of generality, belonging to a large tribe of animals, or 
rather to various species of that tribe, is the poisonous tooth 
of serpents. 
I. The fang cf a viper is a clear and curious example 
of mechanical contrivance. [PI. XXIII. fig. 4, 5.] It is a 
perforated tooth, loose at the root: in its quiet state, lying 
down flat upon the jaw, but furnished with a muscle, which 
with a jerk, and by the pluck as it were of a string, sud¬ 
denly erects it. Under the tooth, close to its root, and 
communicating with the perforation, lies a small bag con¬ 
taining the venom. When the fang is raised, the closing of 
the jaw presses its root against the bag underneath, and the 
* Much obscurity still exists concerning the exact purpose which the 
air-bag is intended to perform. But with regard to the manner in which 
it is supplied with air, there seems no reason to doubt that it is effected 
by a secretion from the blood. It is an established fact in physiology, 
that many of the internal surfaces of the body have the power of producing 
gases in this way. In the air-bag of many fishes a very vascular organ is 
found which has been called the air-gland; and in some species vessels 
have been discovered conveying the air from this gland into the cavity of 
the bag. Even where this gland does not exist, it is probable that the in¬ 
ternal surface of the bag may perform the same office.— Ed. 
