In his presidential address to the Entomological Society in 1872 Wallace made some special allusion to Spencer's theory of the origin of instincts, and on receiving a copy of the address Spencer wrote: "It is gratifying to me to find that your extended knowledge does not lead you to scepticism respecting the speculation of mine which you quote, but rather enables you to cite further facts in justification of it. Possibly your exposition will lead some of those, in whose lines of investigation the question lies, to give deliberate attention to it." A further proof of his confidence was shown by asking Wallace (in 1874) to look over the proofs of the first six chapters of his "Principles of Sociology" in order that he might have the benefit of his criticisms alike as naturalist, anthropologist, and traveller. This brief reference to the illustrious group of men to whom we owe the foundations of this new epoch of evolutionary thought--and not the foundations only, but also the patient building up of the structure upon which each one continued to perform his allotted task--and the prefatory notes and the footnotes attached to the letters will serve to elucidate the historical correspondence between Darwin and Wallace which follows. PART II (_Continued_) II.--The Complete Extant Correspondence between Wallace and Darwin [1857--81] "I hope it is a satisfaction to you to reflect--and very few things in my life have been more satisfactory to me--that we have never felt any jealousy towards each other, though in some senses rivals. I believe I can say this of myself with truth, and I am absolutely sure that it is true of you."--DARWIN to Wallace. "To have thus inspired and retained this friendly feeling, notwithstanding our many differences of opinion, I feel to be one of the greatest honours of my life."--WALLACE to Darwin. "I think the way he [Wallace] carries on controversy is perfectly beautiful, and in future histories of science the Wallace-Darwin episode will form one of the few bright points among rival claimants."--ERASMUS DARWIN to his niece, Henrietta Darwin, 1871. The first eight letters from Darwin to Wallace were found amongst the latter's papers, carefully preserved in an envelope on the outside of which he had written the words reproduced on the next page. Neither Wallace's part of this correspondence, nor the original MS. of his essay "On the Tendency of Varieties to Depart Indefinitely from the Original Type," which he sent to Darwin from Ternate, has been discovered. But these eight letters from Darwin explain themselves and reveal the inner story of the independent discovery of the theory of Natural Selection.