Dear D^r. Darwin

You will be glad to hear that I have been successful in obtaining the Post of Assistant-Keeper in the Zool. Dept. of the British Museum, for which you were so kind as to give me a testimonial.¹

I have lately (i.e. for the last year or two) had an opportunity of studying the Heterocerous Lepidoptera much more closely than formerly, and I find the scent-fans spoken of by Fritz Müller extremely common, particularly upon the legs of moths: strigillating organs occur in all parts in the form of drums, bladders, rasps, and in all sorts of forms: most of the Zygænidæ have a drum-like apparatus at the base of the abdomen, somewhat as in Cicada; this is probably an organ of sound.²

The Genus Sphingomorpha, among the Noctuites, has a bladder-like organ upon its legs which are also provided with enormous radiating fans of hair.³

For anybody who had the time to devote to the study of these structures and their modifications in allied species, there would be an almost endless field for interesting research: perhaps after all no new facts would be brought to light however.

With many thanks for favours past, and the hope that I may yet live to be in some measure useful to you or at anyrate to the Science which you have done so much to advance | Believe me to be | Very sincerely yours | Arthur G Butler