Dear Sir

I have deferred replying to your letter on the subject of rats until now hoping I might have been able to find notes which I feel confident I made on the very point of your inquiry but which I am sorry to add I cannot put my hand upon.¹ for many years I kept rather a large colony of rats, embracing all the colored varieties of the common rats as well as the old english black rat— my impression is that the male sex predominated, that they are altogether a lecherous race the males irritable & pugnacious & the stronger ones admitting of no rivalry in the Harem and consequently disregarding in any shew of preference evinced by the Ladies themselves—who nevertheless I am disposed to think sometimes carried their point—² The females (like rabbits) will receive the male immediately after parturition and also like them occasionally destroy devour their own offspring— I observed that the black & brown rat did not do well together but if paired & put by themselves they then bred freely—the enlarged ear & elongated tail generally well marking the admixture of the black blood— One thing struck me as being rather singular—viz I had rats of all the ordinary colors black, white & brown & also pied varieties—their destiny being chiefly food for an Eagle I then had—which aided by scofulous & malignant tumours sometimes reduced my numbers to a low ebb   on one of these occasions I was left with only one black & white or pied one— and thinking the party colored would surely be reproduced from the Black & White (self.) stock I did not hesitate to destroy the last one, but to my astonishment I never had another until after months had elapsed and my stock from disease reduced to white females[,] I captured a male brown wild one—which lived in peace & love & in due course young family branches sprung up all being of the natural brown color—but on the second cross that is the young of the male brown associating with the pure white—the produce broke out into all the original colors and in one batch might be seen pure black & white as well as the mixed black & white & white & brown pied ones—and so long as the colony existed there was no want of the party colored variety—

Fearing I may have bothered you by my prolixity | I am | Yours truly | John Bush

Charles Darwin Esqr—