Dear M^r Darwin

I have got an idea which I am endeavouring to support by collecting materials of various kinds, & I take the liberty of writing to you to ask if you can assist me. It is this.— that mimetic forms of animals have arisen through the direct cause of prenatal impressions received through the sense of sight; & aided by natural selection.

The grounds for this idea are these

1) the human fœtus is frequently affected by the sight of objects which produce shocks upon the mother.— this is pooh-poohed by many but I think, I have succeeded in establishing it, nevertheless.¹

2^d) Cases amongst animals   a cow A pregnant by Bull B is, however, kept in a field with C (Bull or Cow or Bullock) The result is that the calf may resemble C more than B.

Virgil states somewhere, but have not to hand to refer that if a mare is to bring forth a particular color place such a colored animal before her while being covered by the stallion.—²

compare Jacob’s rod.—³ &c &c

Now I want to collect cases from Breeders of cattle, if possible; & knowing from y^r writings that you had many communications from them on other points,—I was anxious to know if they stated anything to the above effect. & if so whether you would kindly let me hear it.

No case where Pangenesis could apply is of any use. For I want to try & substantiate my idea, where there has been no connection at all: no hereditary descent &c. &c all of which cases would be explained by Pangenesis.⁴

If you have no instances to refer to, could you oblige me with the names & addresses of those breeders with whom you have had correspondence? You will see that my idea is that in consequence of animals constantly living in the same localities & surrounded by the same objects generation after generation; the fœtus has by the slow accumulation of mental force—gradually become assimilated in form or appearance to the surrounding objects.—

Y^rs very truly | Geo Henslow