GENERAL CONCLUSIONS. 789 



organisms. 1 From the demonstration of this principle, which I 

 then satisfied myself was associated with and dominated by that 

 of ' adaptation to purpose,' the step was plain — to me inevitable — 

 to the conception of the operation of a secondary cause of the 

 entire series of species, whether of plants, or vertebrates, or other 

 groups of organisms, such cause being the servant of predeter- 

 mining intelligent Will. 2 



But, besides 'derivation' or ' filiation,' another principle in- 

 fluencing organisation became recognisable in the course of studies 

 and researches on Invertebrate animals. To this principle, as 

 more especially antagonistic to the theological idea, I gave the 

 name of ( irrelative repetition ; ' sometimes also, as it prevailed 

 most in plants and zoophytes, of ( vegetative repetition.' 3 The 

 demonstrated constitution of the vertebrate endoskeleton, as a 

 series of essentially similar segments, out of which, as corollary, 

 came the power of enunciating not only ( special ' but ( general ' 

 and ' serial ' homologies, appeared to me to illustrate also the law 

 of irrelative repetition. The recurrence of similar segments in 

 the spinal column and of similar elements in a vertebral segment, 

 struck me as analogous to the repetition of similar crystals as the 

 result of polarizing force in the growth of an inorganic body. 4 



Accordingly, these results of extensive, patient, and unbiassed 

 inductive research — or, if there were a bias, it was toward 

 Cuvier — swayed with me in rejecting the principle of direct or 

 miraculous creation, and in recognising a ( natural law or secon- 

 dary cause ' as operative in the production of species ' in orderly 

 succession and progression.' 5 



§ 424. Succession of Species, broken or linked? — To the hypo- 

 thesis that existing are modifications of extinct species Cuvier re- 

 plied, that, in every mooted form of transmutation, the species 

 were made to alter by small degrees, and that, therefore, traces of 

 such gradual modifications were due from the fossil world : — ' You 

 ought,' he said, 'to be able to show, e. g., the intermediate forms 

 between the Palaeotherium and existing hoofed quadrupeds.' 6 



1 Such ' ideal type ' must not be confounded with the so-called ' types ' supposed 

 to be exemplified by certain living species. Arguments against the latter vague and 

 ill-defined ideas are of no weight against the former, and indicate a certain obtuse- 

 ness of apprehension in the objector. See cccxxvi". p. 31. 



8 cxli. (1849) p. 86. 



* ccxlix. p. 641 (1843); and vol. i. Preface, p. ix. 



4 cxl. p. 171. * cxli. loc. cit. 



6 ' Cependant on peut leur repondre, dans leur propre systeme, que si les especes ont 

 change par degres, on devroit trouver des traces de ces modifications graduelles; 

 qu'entre le palseotherium et les especes d'aujourd'hui Ton devroit decouvrir quelques 

 formes intermediates, et que jusqu'a present cela n'est point arrive.' — cxxxix- 

 tom. i. p. lvii. 



