Responds to CJFB’s criticisms of the Origin [see 2669].

If CD’s theory is a satisfactory explanation of the "principles of Homology, and of Embryology, and Rudimentary organs", the difficulty in imagining the transitions between classes of beings should not weigh against the understanding it provides such large classes of facts. Defends natural selection against criticism that it is not a vera causa. Comments on "Degeneracy", extinction of intermediate forms, and the effect of theory in natural history in opening up new fields of inquiry and giving rational instead of theological explanations of facts.