AXXIVEKSAEY ADDRESS OF THE TBESIDEXT. xlix 



want of space enough — for terrestrial physics are bound up with 

 cosmical vicissitudes, — and through want of a sufficiently complete 

 sequence in time ; for the " chain of life " (if that be a safe expres- 

 sion) may be so broken by the destruction of links, that no art can 

 reunite it. 



Is there such a chain of life in existence ? Has such ever ex- 

 isted ? Is the actual life of the globe truly descended by ordinary 

 processes from the earlier systems which geology has brought to 

 light, so as in this sense to constitute such a chain ? 



We may confidently declare that in the actual system of nature 

 no such complete chain can be traced ; no possible art of arrange- 

 ment can present plants and animals in one continuous series from 

 a lower to a higher type. Plants cannot be thus placed alone ; ani- 

 mals cannot be so placed. Not even the greater divisions of plants 

 or animals admit of exact collocation in linear series. What we 

 find are groups of allied forms, better represented by circular areas 

 than by straight lines, having analogies which point in different 

 directions, — and combinations of these into families, orders, and 

 classes, through which some general types of structure can be traced, 

 with limited deviations and modifications in all directions, often 

 suited in a remarkable way to the particidar destiny of the creatures 

 which manifest them. 



The classes or greater types to which we thus refer the largest 

 number of groups of existing nature were the same at all periods 

 when they existed at all — for some of the classes appear to be totally 

 absent from the earliest deposits. Some existing families and orders 

 are unknown in the strata ; and some which do occur there are no 

 longer living*. Finally, while several genera of animals have left 

 traces of their existence in every past great geological period, and 

 are still riving, many have come into being and have passed away in 

 each successive period, — their places being either left vacant or re- 

 placed by others of the same natural family, order, or class, or by 

 some group having other general affinities combined with peculi- 

 arities which .serve as substitutes for the special functions of tho 

 perished races. 



The idea of definite general types of structure, represented in all 



* Professor Owen has prepared a full classification of fossil reptiles, in IS 



orders, of which 8 appear i«> be «\t in<t, ami ."> an- both fousil and recent (Rep. 

 Brit Assoc. 1 -.V. M. Tlie following brief summary will explain thia classification: — 



< !;ii!'MV])]mla Carlxmiferoufl. 



Labyrinthudontia ... TrissSlO? 



Ichniyopterygia ... lias to Chalk. 



B auropter y g ia Trias to Chalk. 



Anomodontia Xriaasia. 



Pterosnuria Lias to Chalk. 



Theoodontia Triassio. 



Dmoeanria tiaa, QreensancL 



Orocodflia Lias to modern sea.*. 



Lncertilia < »< >)it i«-. Oretaoeous, Tertiary, Modern. 



( hpUdia Tertiary and dting. 



Clu-lonia Triassio, Oolitic, Cretaceous, Tertiary, lining. 



lJatraehia Oolitic?, Tertiary, living. 



