404 OBJECTIONS TO THE THEORY OF CHAP. xx. 



zoophagous mollusca discharged the functions afterwards per 

 formed by an inferior order in the secondary, tertiary, and post- 

 tertiary seas. But I have never seen this view suggested as 

 adverse to the doctrine of progress, although much stress has 

 been laid on the fact, that the Silurian brachiopoda, creatures 

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

 ing lamellibranchiate 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 organised as the belemnite and 

 other dibranchiate cephalopods which afterwards appeared, 

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

 may infer that the simplest forms of the cephalopoda took 

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

 this view, we must not forget that there are living cephalo 

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

 parts, whether external or internal, and which .eould 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 being, in 

 order to avail ourselves of this argument in favour 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 generalisation, 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 favourite dogma, somewhat beyond the limits which 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 

 specialisation of organs as represented by the successively 





