132 ORIGIN OF SPECIES 



from d"; &", and f*, from having diverged at an earlier 

 period from a^ will be in some degree distinct from the three 

 first-named species; and lastly, o", i"" and w" will be nearly 

 related one to the other, but, from having diverged at the first 

 commencement of the process of modification, will be widely 

 different from the other five species, and may constitute a 

 sub-genus or a distinct genus. 



The six descendants from (I) will form two sub-genera or 

 genera. But as the original species (I) differed largely from 

 (A), standing nearly at the extreme end of the original 

 genus, the six descendants from (I) will, owing to inherit- 

 ance alone, differ considerably from the eight descendants 

 from (A) ; the two groups, moreover, are supposed to have 

 gone on diverging in different directions. The intermediate 

 species, also (and this is a very important consideration), 

 which connected the original species (A) and (I), have all 

 become, excepting (F), extinct, and have left no descend- 

 ants. Hence the six new species descended from (I), 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 pro- 

 duced 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 broken lines, 

 beneath the capital letters, converging in sub-branches down- 

 wards towards a single point ; this point represents a species, 

 the supposed progenitor of our several sub-genera and 

 genera. 



It is worth while to reflect for a moment on the character 

 of the new species f", 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 affinities to the other fourteen new species will be of 

 a curious and circuitous nature. Being descended from a 

 form which stood between the parent-species (A) and (I), 

 now supposed to be extinct and unknown, 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 character from the type of their 



