Comments on forthcoming edition [7th (1847)] of CL’sPrinciples. Mentions other books relevant to CL’s needs by Hooker, H. G. Bronn, Edward Forbes, and J. G. Kölreuter. Discusses his own books on volcanoes and the geology of S. America.

Mentions expected visit to Down by the Lyells.

Grateful for AH’s long letter and suggestions. Delighted at what he says about "complemental males". CD feared no one would believe in them but now that Owen, Dana, and AH accept them, he is content.

Agrees with AH on cross-impregnation; has collected facts on this head but has done nothing with them.

AH’s paper onAlcippe[Ann. & Mag. Nat. Hist.2d ser. 4 (1849): 305–14] caused him to lose sleep over its anomalous structure.

Thanks WDF for his offer of assistance in collecting varieties of poultry. Describes his needs. He will raise his own pigeons.

Often doubts whether, despite all help, the problem of species will not overpower him.

Draft of queries on the varieties of hollyhocks. [To be transmitted to William Chater by JSH; probably enclosed with1778.]

Hybrids ofPhasianus versicolorbreed freely between themselves as well as with common pheasants. Has been assured that hybrids between mallards and pintails are sometimes fertileinter se.