I enclose two diagrams showing the sort of manner I CONJECTURE that mammals have been developed. I thought a little on this when writing page 429, beginning, "Mr. Waterhouse." (Please read the paragraph.) I have not knowledge enough to choose between these two diagrams. If the brain of Marsupials in embryo closely resembles that of Placentals, I should strongly prefer No.2, and this agrees with the antiquity of Microlestes. As a general rule I should prefer No.1 diagram; whether or not Marsupials have gone on being developed, or rising in rank, from a very early period would depend on circumstances too complex for even a conjecture. Lingula has not risen since the Silurian epoch, whereas other molluscs may have risen. Here appear two diagrams. Diagram I. A - Mammals, not true Marsupials nor true Placentals. - 2 branches - Branch I, True Placental, from which branch off Rodents, Insectivora, a branch terminating in Ruminants and Pachyderms, Canidae and terminates in Quadrumana. - Branch II, True Marsupial, from which branches off Kangaroo family an unnamed branch terminating in 2 unnamed branches and terminates in Didelphys Family. Diagram II. A - True Marsupials, lowly developed. - True Marsupials, highly developed. - 2 branches - Branch I, Placentals, from which branch off Rodents, Insectivora, a branch terminating in Ruminants and Pachyderms, Canidae and terminates in Quadrumana. - Branch II, Present Marsupials, splitting into two branches terminating in Kangaroo family (with 2 unnamed branches) and Didelphys family. A, in the two diagrams, represents an unknown form, probably intermediate between Mammals, Reptiles, and Birds, as intermediate as Lepidosiren now is between Fish and Batrachians. This unknown form is probably more closely related to Ornithorhynchus than to any other known form. I do not think that the multiple origin of dogs goes against the single origin of man... All the races of man are so infinitely closer together than to any ape, that (as in the case of descent of all mammals from one progenitor), I should look at all races of men as having certainly descended from one parent. I should look at it as probable that the races of men were less numerous and less divergent formerly than now, unless, indeed, some lower and more aberrant race even than the Hottentot has become extinct. Supposing, as I do for one believe, that our dogs have descended from two or three wolves, jackals, etc., yet these have, on OUR VIEW, descended from a single remote unknown progenitor. With domestic dogs the question is simply whether the whole amount of difference has been produced since man domesticated a single species; or whether part of the difference arises in the state of nature. Agassiz and Co. think the negro and Caucasian are now distinct species, and it is a mere vain discussion whether, when they were rather less distinct, they would, on this standard of specific value, deserve to be called species.