D^r Sir

With regard to M^r Marshalls statement respecting the Polynesian Lice,¹ it is a very extraordinary statement, & I cannot see any reason why the Lice of one Human being should not live upon another! It is a fact that the parasites of one Genus of animals do not live upon animals of another Genus. Swine upon the Horse or Ass or Ass upon the Ox—or Horse, Deer   The same with Birds. Species of the same Genus as the various Ducks have frequently the same Louse   again some of the smaller Passerine Birds. But the Goose & Swan have not the same Louse or that of the Duck or Merganser. As to the identity of the same pediculus on different Races of Men—this is a question of some perplexity. And the first question to decide is are the different races of men varieties only of one Genus or Species! I presume the former, & if so, the differences which exist & are constant in the characters of the Lice of these varieties, are not greater than we find in the races themselves, or in the varieties of the Genus Canis, or Columba, or Gallus. Yet the same species of Lice infest the different varieties of Fowl, Dogs & Pigeons.² M^r Andrew Murray has paid more attention to this subject, than anyone else in Britain whose paper I send you, from which you will perceive, there are well marked characters which distinguish the anterior legs & antennæ of the Lice of different Races as also the colour—, but as he truly observes, these are not greater, than those of the Races themselves ∴ if we cannot believe that they are any thing more than varieties, the same will apply to the Parasites, which also remain fixed!³ I think it very probable M^r Marshalls statement as to the darker colour & difference in appearance: to a general observer, may be correct enough!⁴ The questionable point is their not living upon the English Sailors!. (D^r Milligan,⁵ who resided many years in Tasmania informed me that the aborigines of Tasmania stated to him, that until introduced by Europeans they had never seen the Louse on the Human body! & he had no reason to doubt their veracity! The natives wear no clothes whatever & the women shaved their heads &c— & the men although they wore long hair, so besmeared it with fat & red ochre, as to render it altogether unfit for the abode of even a Louse.

M^r Murray describes two varieties of Australian Lice, which differ in colour &c from the European. ⁶ are we to suppose the Australian Lice are an Introduced from some other race? or aboriginal. if the latter, It is difficult to believe the Tasmanians have been excepted from Parasites. I should rather have suspected the smearing of the Hair was to destroy or extirpate them! and if the women shaved the hair this very practice was adopted by the Egyptian Priests to keep themselves free from vermin!— I believe the Human races in every part of the world have Lice, which may offer slight modifications of character! But I would not commit myself to decide, whether we shall call these specific characters or not. The transition between species in some instances is so gradual that it becomes difficult to say where the variety or Species, begin or terminate!— I fear you will not obtain much information from this rambling note, but any grain is quite at your service.—

Believe me | D^r Sir | Yours very truly | Henry Denny

Charles Darwin Esq | &c—

P.S. I shall be glad of M^r Murrays Paper back again when you have done with it.