ANNIVKRSARY ADDRESS OF THE PRESIDENT. Ixxix 



pose in the world's cecoaomy. Paradoxical must be the mind of the 

 man, a mind without eyes, who in the present state of research would 

 deny the limitation of natural groups to greater or less, but in the 

 main continuous, areas or sections of geological time. Now, that 

 greater and lesser groups — genera, subgenera, families, and orders, 

 as the case may be — or, in truer words, genera of different grades of 

 extent — have replaced others of siinilar value and served the same 

 purpose or played the same -part, is so evident to every naturalist ac- 

 quainted with the geological distribution of animals and plants, that 

 to quote instances would be waste of words. This replacement is 

 substitution of group for group — a phsenomenon strikingly conspi- 

 cuous on a grand scale when we contrast the palseozoic with the after- 

 faunas and floras. A single instance of these greater substitutions 

 may be cited to assist my argument, viz. the substitution of the La- 

 meliibranchiata of later epochs by the Palliobranchiata during the 

 earlier. In this, as in numerous other instances, it is not a total re- 

 placement of one group by another that occurred ; both groups were 

 represented at all times, but as the one group approached a minimum 

 in the development of specific and generic types, the other approached 

 a maximum, and vice versa. I think few geologists and naturalists 

 who have studied both the palaeozoic and the after — I must coin a word 

 — neozoic mollusca will doubt that a large portion of the earlier Bra- 

 chiopoda — the Productidee for example — performed the offices and 

 occupied the places of the shallower-water ordinary bivalves of suc- 

 ceeding epochs. 



Now in this substitution the replacement is not necessarily that of 

 a lower group in the scale of organization by a higher. There is an 

 appearance of such a law in many instances that has led over and 

 over again to erroneous doctrines about progression and development. 

 The contrary may be the case. Now that we have learned the true 

 affinities that exist between the Bry ozoa and the Brachiopoda, we 

 can see in these instances the zoological replacement of a higher by 

 a lower group, whilst in the former view, equally true, of the replace- 

 ment of the Brachiopoda by the Lamellibranchiata, a higher group is 

 substituted for a lower one. Numerous cases might he cited of both 

 categories. 



But can we not find something more in these replacements and in- 

 terchanges than mere substitution, which is a phsenomenon mani- 

 fested among minor and major groups within every extended epoch ? 

 Is there no law to be discovered in the grand general grouping of the 

 substitutions that characterize the palaeozoic epoch when contrasted 

 with all after-epochs considered as one, the Neozoic 1 It seems to 

 me that there is, and that the relation between them is one of con- 

 trast and opposition — in natural-history language, is tiie relation of 

 Polarity. 



The manifestation of this relation in organized nature is by con- 

 trasting developments in opposite directions. The well-known and 

 often-cited instance of the opposition progress of the vegetable and 

 animal series, each starting from the same point — the point at which 

 the animal and vegetable organisms are scarcely if at all distinguish- 



