To B. D. Walsh   9 June 1868

My dear Sir

I am very much obliged for your letter of May 1^st, chiefly about Anthocaris.¹ I had already introduced this genus into my M.S. discussion, but I shall probably be very glad to make use of the new facts which you have given me.²

It has occurred to me that you might perhaps whilst collecting, observe one subject for me without much trouble. I have lately been examining the stridulating apparatus in lamellicorns; & I am surprized to find it in a totally different position in Oryctes & Geotrupes.³ I have not yet examined enough specimens, but the organ seemed more developed in the male Oryctes than in the female.⁴ Now if you catch any m. & f. lamell. will you observe whether the f. can squeak or grate, or whether it does so louder than the male. If so, could you send me a m. & f. named. Does Trox exist with you? As far as I can make out with dead specimens, it grates by rubbing the spinose tibia of middle legs on the edges of the Elytra; & it seems to have no proper stridulating apparatus.⁵

Many thanks for your Report. I agree with your criticism on my expression; as far as I remember I used it merely because others might make a similar objection.⁶

This Report of yours must have cost you an immense quantity of labour. I am still at work & shall continue so for many months on the sexual differences of animals.⁷

With all good wishes believe me | my dear Sir | yours sincerely | Charles Darwin