236 TROOFS OP DESIGN. 



chanical contrivances, more obviously adapted to a definite 

 purpose, than can be found in shells of simpler character. 

 Secondly, because the use of many of their parts can be 

 explained, by reference to the economy and organization of 

 the existing animals, most nearly allied to the extinct fossil 

 genera and species with which we are concerned. And, 

 thirdly, because many of these chambered shells can be 

 shown, not merely to have performed the office of ordinary 

 shells, as a defence for the body of their inhabitants ; but 

 also to have been hydraulic instruments of nice operation, 

 and delicate adjustment, constructed to act in subordination- 

 to those universal and unchanging Laws, which appear to 

 have ever regulated the movement of fluids. 



The history of Chambered shells illustrates also some of 

 those phenomena of fossil conchology, which relate to the 

 Hmitation of species to particular geological Formations;* 

 and affords striking proofs of the curious fact, that many 

 genera, and even whole families, have been called into ex- 

 istence, and again totally annihilated, at various and suc- 

 cessive periods, during the progress of the construction of 

 the crust of our globe. 



The history of Chambered Shells tends farther to throw 

 light upon a point of importance in physiology, and shows- 

 that it is not always by a regular gradation from lower to 

 hiofher degrees of organization, that the progress of life 

 has advanced, during the early epochs of which geology 

 takes cognizance. We find that many of tlie more simple 

 forms have m.aintained their primeval simplicity through 

 all the varied changes the surface of the earth has under- 

 gone : whilst, in other cases, organizations of a higher order 

 preceded many of the lower forms of animal life; some of 



* Thus, the Nautilus multicarinatus is limited to strata of tlie Transition 

 formation ; the N. bidorsatus to the Musclielkalk ; N. obesus, and N. linea- 

 tus, to the Oolite Formation ; N. elcgans, and N. undulatus, to the Chalk.. 

 The divisions of the Tertiary formations have also species of Nautili pccu» 

 liar to themselves. 



