120 STATE OF DEVELOPMENT OP [Chap. XL 



southern hemisphere has become wild in any part of 

 Europe, we may well doubt whether, if all the produc- 

 tions 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 Zea- 

 land. Yet the most skilful naturalist, from an exami- 

 nation 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 embryological de- 

 velopment of existing forms. This view accords ad- 

 mirably 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 embryological character of 



