162 AFFINITIES AND GEOGRAPHICAL 



The dibranchiate belemnites commence 



in the oolitic epoch, ushering in the jD 



sepise, the highest of all the cephalopo- ^ 



dous orders, and which have since con- o ^ 



tinued to exist. 



It is worthy of remark that, in the | 



succession of rocks, the forms of the -f. 



cephalopoda change much more abruptly 



than appears to be the case with other rt 



less organized mollusca ; that is, there jj 



are more Decided as well as more fre- .2 

 quent examples of what geologists call 



change of species in this class than in 



others. This is only one of the many =g ^ 



proofs of law in these phenomena. On e 



the theory of interferences, why should 



there be entire renewals of some sets w 



of animals and not of others? On | .2 



the theory of law, we only see each -i 



line of organic being undergoing the 



modifications appropriate to its special * 



constitution, in connexion with the effi- g, | | | 



cacyupon that constitution of external | | !~<i| 



conditions. g H cq 



When we consider the Invertebrate 



animals in this arrangement, the advances o -3 -2 



made in portions of the Animal Kingdom | | | 



before the end of the Silurian era, appear | g ^ ^ 

 in a very different light from what they 



do while we entertain the erroneous no- | . 



tion that there is but one chain of being. & R J- | 



The annexed tabular view will make this ~ & ^ 



readily and abundantly plain. Those ani- o 

 mals which, though hypothetically con- % 



cerned in the genealogy, are not actually t* % 



found in a fossil state, but for whose non- g | d 



appearance as fossils reasons are given, ^ d ^ 

 are expressed in italics. 



