404 OBJECTIONS TO THE THEORY OF CHAP. XX. 



zoopbagous mollusca discharged the functions afterwards j)er- 

 formed by an inferior order in the secondary, tertiarj^, and 

 post-tertiary seas. But I have never seentbis view suggested 

 as adverse to the doctrine of progress, although much stress has 

 been laid on the fiict that the Silurian brachiopoda, creatures 

 of a lower grade, formerly discharged the functions of the exist- 

 ing lamellibrancbiate bivalves, which are higher in the scale. 



It is said truly that the ammonite, orthoceras; and nautilus 

 of these ancient rocks were of the tetrabranchiate division, 

 and none of them so highly organized as the belemnite and 

 other dibranchiate cephalopods which afterwards appeared, 

 and some of which now flourish in our seas. Therefore, we 

 ma}^ infer that the simplest forms of the cejibalopoda took 

 precedence of the more complex in time. But if we embrace 

 this view, w^e must not forget that there are living cephalo- 

 poda, such as the octojiods, which are devoid of any hard 

 parts, whether external or internal, and which could leave 

 behind them no fossil memorials of their existence; so that 

 we must make a somewhat arbitrary assumption, namely, 

 that at a remote era no such dibranchiata were in beins;, in 

 order to avail ourselves of this argument in ftxvor of pro- 

 gression. On the other hand, it is true that in the "primordial 

 zone" of Barrande not even the shell-bearing tetrabranchiates 

 have yet been discovered. 



In regard to plants, although the generalization, above 

 cited, of M. Adolphe Brongniart (p. 398) is probably true, 

 there has been a tendency in the advocates of progression to 

 push the inferences deducible from known facts, in support of 

 their ftivorite dogma, somewhat beyond the limits Avhich the 

 evidence justifies. Dr. Hooker observes, in his recent intro- 

 ductory essay on the flora of Australia, that it is impossible to 

 establish a parallel between the successive appearances of 

 vegetable forms in time, and their complexity of structure or 

 specialization of organs as represented by the successively 



