.30 FINAL CAUSES. 



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, that 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 medium ? 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 propi- 

 tious, and by means of which it is wafted along 

 the surface of the sea, but which it quickly 

 retracts in unfavourable circumstances, is not her 

 design similar to that of the human artificer, 

 when he equips his bark with sails, and provides 

 the requisite machinery for their being hoisted 

 or furled with ease and expedition ? 



The maker of an hydraulic engine places 

 valves in particular parts of its pipes and cis- 

 terns, with a view to prevent the retrograde 

 motion of the fluids which are to pass through 

 them. Can the valves of the veins, or of the 



