310 SUCCESSION OF THE Cuap. X. 



any considcriiblc number -would be enabled to seize on jilaces 

 now occupied by our native plants and animals. Under this 

 point of view, the productions of Great Britain stand much 

 hioher 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 hif^hly-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 Avith 

 the embryological development of existing forms. This view 

 accords admirably well with our theory. In a future chapter I 

 shall attempt to show that the adult differs from its embryo, 

 OM'ing to variations supervening at a not early age, and being 

 inherited at a corresponding age. This process, while 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 ancient and less modified condition of the 

 animal. This view may be true, and yet may never be capable 

 of full proof. Seeing, for instance, that the oldest known mam- 

 mals, reptiles, and fishes, strictly belong to their proper classes, 

 though some of these old forms are in a slight degree less dis- 

 tinct 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 embryological character of the Yertebrata, 

 until beds rich in fossils are discovered far beneath the lowest 

 Silurian stratum — a discovery of which the chance is small. 



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

 during the later Tertiary Periods. 



Mr. Clift many years ago showed that the fossil mammals 

 from the Australian caves were closely allied to the living mar- 

 supials of that continent. In South America, a similar relation- 

 ship is manifest, even to an uneducated eye, in the gigantic 

 pieces of armor, like those of tlie armadillo, found in several 

 parts of I^a Plata ; and Prof. Owen has shown in the most 

 striking manner that most of the fossil manmials, buried there 

 in such lunnbers, are related to South American t^-pes. This 

 relationship is even more clearl}' seen in the wonderful collection 

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

 Urazil. I was so much injprcssed with these facts that I 



