This category of characters consists chiefly in the relation of individuals to one another and to their surroundings, and in the relative dimensions and proportions of parts. These characters are no less permanent and constant in the different species of the human family than in those of any other family in the animal kingdom, and my observations upon the cross-breeds in South America have convinced me that the varieties arising from contact between these human species, or so-called races, differ from true species just as cross-breeds among animals differ from true species, and that they retain the same liability to revert to the original stock as is observed among all so-called varieties or breeds.” Our visit to Mauhes will be the pleasanter and doubtless the more successful, because Dr. Epaminondas, who has already done so much to facilitate the objects of the expedition, takes this opportunity of visiting a region with which, as President of the province, he is desirous of becoming acquainted. He is accompanied by our host, Mr. Honorio, whose house has been such a pleasant home for us during our stay in Manaos, and also by Mr. Michelis, Lieutenant-Colonel of the National Guard of Mauhes, returning to his home there, after a stay of several weeks in Manaos. Besides these, our party consists of Major Coutinho, Mr. Burkhardt, and ourselves. The position of Mauhes, on the southern side of the Amazons, and its proximity to Manaos and Serpa, may make this excursion especially instructive, with reference to the study of the geographical distribution of the Fishes in the great network of rivers connecting the Rio Madeira and the Rio Tapajoz with the Amazons. ----- Footnote 82: I trust that the motive will not be misunderstood which induces me to add here a translation of the general cards of invitation distributed on this occasion. The graceful expression of a thought so kind, and the manner in which the President merges his own personality in the name of the Province of which he is the administrative head, are so characteristic of his mingled courtesy and modesty, that I am tempted to insert the note, notwithstanding its personal character. Unfortunately, I cannot always do full justice to the kindness shown Mr. Agassiz throughout our journey, or to the general appreciation of his scientific objects, without introducing testimonials into this narrative which it would perhaps be more becoming in me to suppress. But I do not know how otherwise to acknowledge our obligations, and I trust it will be attributed, by candid readers, to the true motive,—to gratitude and not to egotism.