114 BESVLT OF THE ACTION 



posed to have gone on diverging in different directions. 

 The intermediate species, also (and this is a very import- 

 ant consideration), which connected the original species 

 (A) and (I), have all become, except (P), extinct, and 

 have left no descendants. Hence the six new species de- 

 scended from fl), and the eight descendants from (A), 

 will have to be ranked as very distinct genera, or even as 

 distinct sub-families. 



Thus it is, as I believe, that two or more genera are 

 produced by descent with modification, from two or more 

 species of the same genus. And the two or more parent- 

 species are supposed to be descended from some one species 

 of an earlier genus. In our diagram this is indicated by the 

 br9ken lines beneath the capital letters, converging in sub- 

 branches downward toward a single point; this point rep- 

 resents a species, the supposed progenitor of our several 

 new sub-genera and genera. 



It is worth while to reflect for a moment on the charac- 

 ter of the new species i^*, which is supposed not to have 

 diverged much in character, but to have retained the form 

 of (F), either unaltered or altered only in a slight degree. 

 In this case its aflBnities to the other fourteen new species 

 will be of a curious and circuitous nature. Being de- 

 scended from a form that stood between the parent- 

 species (A) and (I), now supposed to be extinct and un- 

 known, it will be in some degree intermediate in character 

 between the two groups descended from these two species. 

 But as these two groups have gone on diverging in charac- 

 ter from the type of their parents, the new species (f") 

 will not be directly intermediate between them, but rather 

 between types of the two groups; and every naturalist 

 will be able to call such cases before his mind. 



In the diagram each horizontal line has hitherto been 

 supposed to represent a thousand generations, but each 

 may represent a million or more generations; it may also 

 represent a section of the successive strata of the earth's 

 crust including extinct remains. We shall, when we come 

 to our chapter on geology, have to refer again to this sub- 

 ject, and I think we shall then see that the diagram throws 

 light on the affinities of extinct beings, which, though 

 generally belonging to the same orders, families or genera, 

 with those now living, yet are often, in some degree, inter- 



