444 PALAEONTOLOGY. 



generalisations, based on rigorous and extensive observation of 

 facts, which have impressed hirn with a conviction of a con- 

 tinuously operative secondary creational power, originating 

 the succession of species, are the following : that of irrela- 

 tive or vegetative repetition ; * that of unity of plan, as 

 demonstrated in the articulate f and vertebrate | types of 

 organisation ; the facts of congenital varieties ; the pheno- 

 mena of parthenogenesis ; § the analogies of transitory embry- 

 onal stages in a higher animal, to the mature forms of lower 

 animals ; the great palseontological fact of the successive 

 coming in of new species, from the period of the oldest de- 

 posits in which organic remains have been found ; such 

 species being limited in time, and never reappearing after 

 once dying out ; the many instances of retention of structures 

 in paleozoic species, which are embryonal and transitory in 

 later species of the same order or class ; the progressive de- 

 parture from a general to a special type, as exemplified in 

 the series of species from their first introduction to the pre- 

 sent time. 



The inductive demonstration of the nature and mode of 

 operation of such secondary continuously operative species- 

 producing force will henceforth be the great aim of the 

 philosophical naturalist. 



The Table (fig. 1 74) expresses the sum of the observations, 

 at the present date, on the successive appearance and geolo- 

 gical relations of the several orders of the Mammalian class. 



The earliest evidences are of small species, which, when- 

 ever they have presented grounds for ordinal determination, 



* Owen, Lectures on the Invertebrata, 8vo., 1843, p. 364. 



f Savigny, Animaux Inverterbres d'Egypte, Descr. de l'Egypt, 4to., vols, 

 xxii and xxiii, 1827. 



| Owen on the Vertebrate Archetype, 8vo., 1848. On the Nature of Limbs, 

 8vo., 1849. < 



§ Owen on Parthenogenesis, 8vo, 1849. 



