FINAL CAUSES. 25 



we found an insect,* shaped like the boat, and 

 moving through the water by successive impulses 

 given to that medium by the action of levers, ex- 

 tending from its sides, and shaped like paddles, 

 having the same kind of movement, and producing 

 the same effects. Could we resist the persuasion 

 that the Artificer of this insect, when forming it of 

 this shape, and providing it with these paddles, had 

 the same mechanical objects in view? Shall we 

 not be confirmed in this idea on finding that these 

 paddles are constructed with joints, which admit 

 of no other motion than that of striking against the 

 water, and of thus urging forwards the animal in 

 its passage through that dense and resisting me- 

 dium? Many aquatic animals are furnished with 

 tails, which evidently act as rudders, directing the 

 course of their progressive motion through the fluid. 

 Who can doubt but that the same intention and 

 the same mechanical principles which guide the 

 practice of the ship-builder, are here applied in a 

 manner still more refined, and with a master's 

 hand ? If Nature has furnished the nautilus with 

 an expansible membrane, which the animal is able 

 to spread before the breeze, when propitious, and 

 by means of which it is wafted along the surface of 

 the sea, but which it quickly retracts in unfavour- 

 able circumstances, is not her design similar to 

 that of the human artificer, when he equips his 

 bark with sails, and provides the requisite machi- 

 nery for their being hoisted or furled with ease and 

 expedition ? 



The maker of an hydraulic engine places valves 



* Such as the Notonecta glauca, Lin., or water boatman, and 

 the Dytiscvs marginalis, or water beetle. 



