My dear Sir

I have been extremely much interested by your letter on Rattle-snakes.—² The subject has always rather fascinated me. By the way can there be any truth in the many accounts of Rattle-snakes fascinating their prey?³ Do they rattle when gazing at their prey & can the poor animals be paralised by fear?— I never could understand from drawing, the rattle, till seeing yours, which makes it quite clear. If not known, is it not a shame that you do not publish your diagram?⁴ The whole contrivance & structure is much more complex than I expected; & I fear it will be impossible to show amongst other snakes any gradation except the vibrating the tail (I did not know of your Black snake having this habit, & am glad to hear it) & the little knob at the end of tail of Trigonocephalus. Nevertheless I will have a look some day at the tails of the Viperidæ in B. Museum for bare chance of any vestige of the concentric ridges which seem to play an important part in retaining the rattle. I presume each new rattle adheres closely to the “matrix” till the period of moulting.— It certainly is a very curious structure; & odiously wonderful to me if it serve merely to warn prey & so injure its possessor.—⁵

With respect to Electrical organs, have you seen M’Donnel’s article in the new Nat. Hist. Review? the discovery (if proved) of these organs in head of Skates seems very interesting.—⁶

Thank you much for telling me your observations on the marks on the face of Vespidæ:⁷ I will show your sketch & consult our great authority on these insects F. Smith of B. Museum.⁸ I shall be curious to know whether anything analogous occurs with our wasps. I particularly value such cases of variation & have already got a large series of cases, & very important they seem to me. Those who believe in creation, will have to say this mark in this animal was thus created; in this other animal that very same mark is due to Variation.

With cordial thanks for your most interesting letter. Believe me, my dear Sir | Yours sincerely C. Darwin