Chap. XIII. CLASSIFICATION. 421 



degree ; tliey may metaphorically be called cousins to 

 the same millionth degree ; yet they differ widely 

 and in different degrees from each other. The forms 

 descended from A, now broken up into two or three 

 families, constitute a distinct order from those de- 

 scended from I, also broken up into two families. Nor 

 can the existing species, descended from A, be ranked 

 in the same genus with the parent A ; or those from 

 I, with the parent I. But the existing genus F 14 may 

 be supposed to have been but slightly modified ; and 

 it will then rank with the parent-genus F ; just as 

 some few still living organic beings belong to Silurian 

 genera. So that the amount or value of the differ- 

 ences between organic beings all related to each other 

 in the same degree in blood, has come to be widely 

 different. Nevertheless their genealogical arrange- 

 ment remains strictly true, not only at the present 

 time, but at each successive period of descent. All 

 the modified descendants from A will have inherited 

 something in common from their common parent, as 

 will all the descendants from I ; so will it be with each 

 subordinate branch of descendants, at each successive 

 period. If, however, we choose to suppose that any of 

 the descendants of A or of I have been so much modi- 

 fied as to have more or less completely lost traces of 

 then parentage, in this case, their places in a natural 

 classification will have been more or less completely lost, 

 — as sometimes seems to have occurred with existing 

 organisms. All the descendants of the genus F, along 

 its whole line of descent, are supposed to have been 

 but little modified, and they yet form a single genus. 

 But this genus, though much isolated, will still occupy 

 its proper intermediate position ; for F originally was 

 intermediate in character between A and I, and the 

 several genera descended from these two genera will 



