My dear Waterhouse

I have read your paper with much interest & it has helped to clear my notions considerably, though I do not think I was one of the very guilty ones, against whom you write.² By the term “link between any two groups” I never understood (, & I rather doubt, whether many naturalists meant much more) a half way link, but merely one in a long series. I think you have done good service in pointing out how rare half-way-links are, if indeed they exist. If they do exist which I doubt we must, I suspect, look back to ancient geological periods.— There is one thing to observe namely that one cannot have a simple species intermediate between two great families, for if such did exist, it w^d form a third natural family. Now amongst vegetables there are some very small families, containing only one or two genera, which certainly seem intermediate between other great families. Now, without you can show to the contrary, the impression on my mind from Owens papers is that Marsupiata form a link (much closer of course to one side than the other) between the Mammalia & Birds & Reptiles—³ And the Monotremata a still plainer link.— These Mammalian groups, partake of some of the important characters (which no one would consider as merely adaptive) of Birds & Reptiles & I cannot see any objection to considering them as links— I do not know, however, whether you would object to calling them so, as long as they are clearly admitted amongst the Mammalia.— You speak rather undecidedly whether all such affinities are “adaptive”.— I quite admit the validity of this distinction, but it appears to me so vague, when applied to organs of such importance as the intestines & teeth of the wombat, that I think you are bound either clearly to define (a tough job I expect) the distinction or to confess that it is vague.—⁴ There is one fact, (which I presume to be a fact) that has long surprised me & is I believe of common occurrence, viz a certain part or organ of a species of a well defined group, resembling closely that part, or organ in another group. Amongst plants it appears to be not very uncommon that a genus in one family has one character of another family. How is this in insects? Owen in describing fossils, is very fond of this method of describing, by saying it has the teeth of this family, the humerus &c of another.— (Do take trouble; if you can spare time; & write me a note on these points)

I have one criticism to make about your circles⁵ —that is that I think you are bound to state that they do not necessarily represent (without you think they do) groups of equal value & though all touching, the affinities are not necessarily equally strong.— I believe infinite harm has been done by these circles, which catch the eye as of equal size, & inevitably lead the mind to suppose they are of equal value— it is by this artifice, as I believe, the possibility of making the Quinarian system appear probible has chiefly rested: Moreover it sh^d be stated by everyone, I think, who indulges in these vicious circles, that confessedly there is no standard to judge of the value of groups.— Who can prove that the woodpecker are not a group of equal value with the Hawks.— I suspect that number of species, ie amount of variation of one common type does silently come into play in estimating the value of groups.—

I admire my own impudence in criticising you & doing this I repeat I think you have done good service in pointing that most or all links are not intermediate but fall into to one or other of the two groups,— Are there are not some forms which show alliances to more than two groups? (a case you do not allude to, which surely is real)— as for your wicked circles, I wish they were all d——d together.

Farewell | Yours impudently | C. Darwin

I saw Owen, after you, & he spoke most warmly & cordially about your affairs—

N.B. This is vilely written letter, but I cannot express myself off-hand—