INTRODUCTION. 9 



place in the animal kingdom, but only exception- 

 ally in the vegetable, where they generally survive 

 in their modifications, and the flora of our own 

 age is much more parallel to the fossil flora than 

 the present is to the fossil fauna. At least the 

 fossil flora exhibits comparatively few types, which 

 are without representation to-day, and rarely 

 startles us with those monstrous forms, which con- 

 stitute to such a great extent the fauna of bygone 

 ages. 



The gradual disappearance of the connecting 

 links, explains the reason why fossil types which 

 have survived to our day, never form continuous 

 lines of variations, like those found in modern 

 types, but exhibit a number of well defined forms 

 isolated by the extinction of the intermediate and 

 transitional ones. An example of this state of 

 things is to be found in the class of Vascular Cryp- 

 togams ; the chief types of which are separated by 

 wide gaps, only partially filled in by the fossil re- 

 mains of extinct connecting forms. 



The whole class has a fragmentary look, and in 

 fact represents only the fragments of a class, once 

 dominant, but now decimated, partly by the in- 

 roads of other lines of evolution, partly by deser- 

 tion, its own members forming for themselves 

 new lines of evolution. 



Quite the reverse is the case with the types pre- 

 dominating at present and not represented in 

 palaeozoic ages. Such groups abound in forms in 

 their earliest development ; in types connected 

 1a 



