The “green silk” referred to some specimens of coal-tar colours sent to show Darwin what modern chemistry had been able to accomplish in the way of artificial colouring matters. They were at that time of particular interest in connection with a discussion which had arisen in Bryanston Street about the so-called “æsthetic” school, which had become rather predominant at the period, and which affected an abhorrence of all brilliant colouring, in spite of the circumstance that nature abounds in the most gorgeous hues, especially in the tropics. The next letter refers to the adoption of the word “phyletic” in the translation of Weismann. “_Dec. 14_ [1878]. “Down. “MY DEAR SIR,--I am very glad that you are making good progress with the book.--You could not apply to a worse person than myself on any philological question. I presume that ‘phyletische’ has been adopted or modified from Häckel. As the latter uses the word, it has nearly the sense of genealogical. It always applies to the lines of descent, and therefore differs somewhat from ‘innate’; for an inherited character, though derived from the father alone or only a single generation, would be innate in the child. I should think ‘phyletic’ would do very well, if you gave the German word and an explanation, in a foot-note. “There has been a delay in answering your letter, but I have just heard from my son who is away from home, and he says that he is sorry but he cannot well spare the time to lecture. “My dear Sir, yours very faithfully, “CH. DARWIN.” Then followed two letters (January 20th, and February 7th, 1879), the first written when Darwin was sending a number of _Kosmos_; the second referring to it and other papers, and asking that his name should be put down as a subscriber to the forthcoming translation of Weismann. Later on the number of _Kosmos_ for May, 1879, was sent, containing (p. 100) Fritz Müller’s paper “_Ituna_ and _Thyridia_.” This paper, although it did not attract sufficient attention at the time, was of the highest importance in relation to the theory of mimicry, as Meldola at once perceived.