CHAP. XI.] ANCIENT AND LIVING FORMS. 291 



ruinate many of the natives. On the other hand, from the fact 

 that hardly a single inhabitant of the southern hemisphere has 

 become wild in any part of Europe, we may well doubt whether, 

 if all the productions of New Zealand were set free in Great 

 Britain, any considerable number would be enabled to seize on 

 places now occupied by our native plants and animals. Under 

 this point of view, the productions of Great Britain stand much 

 higher in the scale than those of New Zealand. Yet the most 

 skilful naturalist, from an examination of the species of the two 

 countries, could not have foreseen this result. 



Agassiz and several other highly competent judges insist that 

 ancient animals resemble to a certain extent the embryos of recent 

 animals belonging to the same classes ; and that the geological 

 succession of extinct forms is nearly parallel with the embryo- 

 logical development of existing forms. This view accords admir- 

 ably well with our theory. In a future chapter I shall attempt 

 to show that the adult differs from its embryo, owing to variations 

 having supervened at a not early age, and having been inherited 

 at a corresponding age. This process, whilst it leaves the embryo 

 almost unaltered, continually adds, in the course of successive 

 generations, more and more difference to the adult. Thus the 

 embryo comes to be left as a sort of picture, preserved by nature, 

 of the former and less modified condition of the species. This 

 view may be true, and yet may never be capable of proof. Seeing 

 for instance, that the oldest known mammals, reptiles, and fishes 

 strictly belong to their proper classes, though some of these old 

 forms are in a slight degree less distinct from each other than are 

 the typical members of the same groups at the present day, it 

 would be vain to look for animals having the common embryo- 

 logical character of the Vertebrata, until beds rich in fossils are 

 discovered far beneath the lowest Cambrian strata a discovery 

 of which the chance is small. 



On the Succession of the same Types within the same Areas, 

 during t/ie later Tertiary periods. 



Mr. Clift many years ago showed that the fossil mammals from 

 the Australian caves were closely allied to the living marsupials 

 of that continent. In South America, a similar relationship is 

 manifest, even to an uneducated eye, in the gigantic pieces ol 

 armour, like those of the armadillo, found in several parts of La 

 Plata; and Professor Owen has shown in the most striking 

 manner that most of the fossil mammals, buried there in such 

 numbers, are related to South American types. This relationship 

 is even more clearly seen in the wonderful collection of fossil 

 bones made by MM. Lund and Clausen in the caves of Brazil 

 I was so much impressed with these facts that I strongly insisted 



