Dear Sir,

I thank you much for having taken so much trouble in describing fully your interesting and curious case of mimickry.¹

I am in the habit of looking through many scientific Journals, and though my memory is now not nearly so good as it was, I feel pretty sure that no such case as yours has been described (amongst the nudibranch) molluscs. You perhaps know the case of a fish allied to Hippocampus, (described some years ago by Dr Günther in Proc. Zoolog. Soc^y.) which clings by its tail to sea-weeds, and is covered with waving filaments so as itself to look like a piece of the same sea-weed.² The parallelism between your and Dr Gùnther’s case makes both of them the more interesting; considering how far a fish and a mollusc stand apart. It w^d. be difficult for anyone to explain such cases by the direct action of the environment.— I am glad that you intend to make further observations on this mollusc, and I hope that you will give a figure and if possible a coloured figure.

With all good wishes from an old brother naturalist,

I remain, Dear Sir, | Yours faithfully, | Charles Darwin.