From J. T. Moggridge   1 February 1873

My dear M^r. Darwin

Your most kind letter which reached me last night gave me the greatest pleasure and encouragement, & I value it very highly.—¹

I must own that as regards instinct I am still in a measure at sea & driven about by seemingly conflicting facts.

I cannot however accept M^r. Wallace’s definition of the term:—“the performance by an animal of complex acts, absolutely without instruction or previously-acquired knowledge”,² for it appears to me that the balance of probability inclines to the explanation according to which instinct, in its rigorously limited sense, is the performance of complex acts without instruction received by the individual, but guided by inherited experience, that is to say by knowledge acquired by & transmitted through its ancestors.

My wish in writing as I did about instinct, was to call attention to the point where experiment and observation might be brought to bear with the best hope of good results, & it appeared to me that M^r. Wallace’s views were well suited to stimulate a wholesome & fruitful opposition.³

I have been much struck lately by the lack of instinct which houseflies display when placed in confinement with a trap-door spider— Far from having any notion as to the hostile character of the spider, they approach it with apparent curiosity & even crawl over it & between its legs, until, finally, they approach its mouth when they are struck down & killed—

This was so in the warm weather & is not due to any torpid condition in the flies.

I am sorry that your letter contained no word of your own health, but I occasionally hear of you through Miss Forster.—⁴

I have been very well on the whole this winter, & have not felt materially the worse for the frequent storms of rain which have greatly interfered with my observations on ants & spiders.

I hope that I need scarcely remind you that I shall always accept with real pleasure any commission within my power to execute in the natural history line which you may be so good as to give me, so pray have no scruple to make any use of me you can.

Believe me | Y^rs. very sincerely | J. Traherne Moggridge.

May I ask you to have the enclosed note posted?⁵