NATURAL THEOLOGY. 257 



These examples mark the attention of the Crea- 

 tor 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 of a viper is a clear and curious 

 example of mechanical contrivance. It is a per- 

 forated 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, suddenly erects it. Under the 

 tooth, close to its root, and communicating with 

 the perforation, lies a small bag containing the 

 venom. When the fang is raised, the closing of 



depths without waste of animal exertion : such is the power of ex- 

 pansion of the air-bladder when relieved from the pressure, that, 

 when a fish is brought up from the greatest depth, it inverts and 

 thrusts out the viscera from the mouth. We do not see, however, 

 that naturalists have adverted to the place of tliis swimming-blad- 

 der. It lies close to the spine, and appears to counterbalance, in 

 some measure at least, the air in the intestines by being thus 

 placed above them. In the cetacea, as the whale, their buoyancy 

 proceeds from the quantity of oil under the skin, especially of 

 their head, and which it has been observed is bestowed in order 

 to ensure their readily coming to the surface to breathe when 

 their natural powers are weakened. For the same reason, that 

 they may raise their heads to the surface, their tails are horizontal. 

 In the jelly-fish, those soft animals which float in sheltered estua- 

 ries, (the physsophora,) there is an air-vessel which they can fill 

 and empty, by which means they rise or sink at pleasure. Others 

 (the villela,) raise a sail. Some of this class propel themselves by 

 taking in water, and suddenly rejecting it. 



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