[63]

From the impossibility, as yet, of distinguishing vars & sp. I look at forms in an incipient species — The evidence convinces me that these occur most in the larger genera (—not always some apparently not in larger & some in smaller) Now what will result of this be.— As we know genera do not go on forever increasing, as we know that extinction has played so great a part— — as indeed extinction almost follows on our theory — (give illustration from Youatt), then it may be asked whether we have any ground, how extinction will act on var. of species on species of genera, on genera in Families I think we have some slight guides.