120 STATE OF DEVELOPMENT OF [Chap. XI. 



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 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 correspondinor 

 age. Tliis 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 



