THE VEGETABLE AND ANIMAL KINGDOMS. 125 



from rushing to the supposition that there has been a very 

 gradual transition of forms, that the first animals of all the 

 various orders were very small and ill-fashioned, and so forth. 

 Such preconceptions, not being verified by the fact, only tend 

 to bewilder us regarding the actual character of that progres- 

 sion of forms which meets us in the pages of the geologist. It 

 must be taken for what it exactly is, and that, as far as we 

 can see, is not a pure, simple series of equal transitions, but a 

 ' plurality of lines, in which there have either been some com- 

 paratively wide leaps, or else certain intermediate species 

 which have been lost to observation. Those whose prejudices 

 lead them to dispute the broad fact of progressive organization, 

 generally rest their objections on points of that kind, either 

 assuming that such are necessary to the idea of progress, or 

 finding that they have been incautiously sanctioned by the ad- 

 vocates of that doctrine. 1 



Leaving for a future section the particulars of the animal 

 scale, which will there lend us further illustration, it may now 

 be observed that, while the external features of the various 

 creatures are so different, there has been traced, throughout 

 large groups of them, a, fundamental unity of organization, as 

 implying, with respect to these groups, that all were constructed 

 upon one plan, though in a series of improvements and varia- 

 tions, giving rise to the special forms, and bearing reference to 

 the conditions in which each animal lives. Starting from the 

 primitive germ, which, as we have seen, is the representative 

 of a particular order of full-grown animals, we find all others 

 to be merely advances from that type, with the extension of 

 endowments and modifications of form which are required in 

 each particular case ; each form, also, retaining a strong affinity 

 to that which precedes it, and tending to impress its own fea- 

 tures on that which succeeds. 



This principle is partly matter of familiar observation. It 

 is obvious to all, that an ordinary mammalian quadruped has 



1 See Proofs and Illustrations, No. 5, The Lower Silurian System 

 is the record of an era of invertebrate animals ; No. 6, The genera of 

 the Lower Silurian era are humble in their respective lines ; No. 7, The 

 early fishes were low both with regard to their class as fishes and the 

 order to which they belong (cartilagines) ; No. 8, In all the orders of 

 fossil animals there is an ascending character from first to last ; No. 9, 

 There is a succession from low to high types in fossil plants, from the 

 earliest strata in which they are found to the highest ; No. 10, The 

 comparatively large bulk of some of the early fossil animals is to be re- 

 garded as a mark of their inferiority in the scale. 



