PRE-DETERMINATION IN NATURE 341 



more complicated kinds of fruit are later inventions, but the 

 additions in these consist mainly of accessories. The essentials 

 of vegetable reproduction were as well provided for from the 

 first. 



The same principle applies to many of the leading forms and 

 types of life, considered as genera or species. While some of 

 these are of recent introduction, others have continued almost 

 unchanged from the remotest ages. Such creatures as the 

 Lingulae, some of the Crustaceans and of the Mollusks, the 

 Polyzoa and some Corals have remained with scarcely any 

 change throughout geological time, while others have dis- 

 appeared, and have been replaced by new types. 



We began this chapter with a consideration of the per- 

 manence of continental areas, and may close with a reference 

 to the same great fact in connection with the continuity of life. 

 Whether with some we attach more importance to the support 

 of the continents by lateral pressure and rigidity, or with others 

 to what may be termed flotation, by virtue of their less density, 

 as compared with that of the lower parts of the earth ; there 

 can be little doubt that both principles have been applied, and 

 that both admit of some vertical movement. Thus the stability 

 of the continents is one of position rather than height, and 

 their internal plateaus as well as their partially submerged 

 marginal slopes have undergone great and unequal elevations 

 and depressions, causing most important geographical changes. 

 Among these are the formation of connecting bridges of shoals, 

 islands, or low land, connecting the continental masses at 

 different periods, and permitting migrations of shallow-water 

 animals and even of denizens of the land. The facts adduced 

 in previous pages are sufficient to show connections across the 

 north of the Atlantic at intervals reaching from the Cambrian 

 to the Modern. 



The conclusion of the whole matter is that there is a fixity 

 and unchangeableness in determinations and arrangements of 



